user8672: Having a correct mindset has been a frustrating endeavor in my chess career. I have some questions regarding how to get into a "correct mindset."
1) I can never seem to play against lower rated players. I am 2350 USCF and I have a higher win rate against 2400s (around 75%) than even 2100-2200s (40-50%). It's hard not to focus on the rating during my games, and it adds a lot of stress because I'm not expected to lose.
2) The last round has always been a struggle for me. A lot of the times I just collapse, especially if I need to win the last round for money or for a title. 
3) I've lost against lower rated players so much that tournaments become stressful. This is mainly due to the fact that if I lose to a lower rated player in round 1, I am doomed to pair down the rest of the tournament. 
I can probably play 500 points better if I could get rid of all this unnecessary stress. The real question is how to get rid of it. Trying to calm down is a paradox. Some of the best games I've played was when I got so absorbed by the position I forget about everything else.
I appreciate all advice. Thanks for reading this post. 

user10348: @user3456... I think your answer suits more, although I am not in a position to conclude. Playing to win is actually riskier than playing for a draw. When I play someone with a lower rating, I tend to end up losing than win, but it gets more challenging when I play someone stronger. I go all out, and end up doing well.
.
To solve it in my own understanding, is to learn to be brutal. Show no mercy, to even a 1300. "Kill them all"

user9627: This worked for me when I was 2030 USCF and was attempting to climb my way to USCF master rating in 1 year. Psychologically I had 2 goals/methods:
1) Play every game based on the board, and try to play the best moves no matter how crazy or complicated they seemed (or how quiet and dry in some cases). Whether my opponent was 1600 or 2450 it shouldn't matter and I should play the same move regardless, since my focus wasn't to beat my opponent but to find the best moves to play. Playing guess the move on thousands of gm games, double checked with engine analysis, helped solidify this into a habit. Also telling myself again and again not to care about the result, but instead to try and have an entertaining game I can learn from.
2) I would always avoid looking at my opponents rating on the pairings, and would tell my friends to NEVER tell me the rating of who I'm playing against. Knowing this would only distract my attention away from the board and trying to find the best moves. If my opponent were Magnus I would still want to aggressively take advantage of anything that seemed to be a mistake, aka not give him the benefit of the doubt on complicated positions, and if my opponent was 1200 I'd still avoid playing aggressively if the position called for quiet moves.
Also as far as your endurance problems I would never eat anything unhealthy during a tournament, only proteins and complex carbohydrates religiously (mixed bean salad, and turkey sandwiches without sauces mainly). I would do my best to get 8 hours of sleep each night and have a light workout each morning if the hotel had an exercise room. Even though my normal lifestyle isn't nearly this good, I'd change my habits for the tournaments to be more competitive.
Another thing I'd attempt to do is get through my first 20 or so moves in under an hour. Even if I didn't know the opening super well I didn't want to waste my energy on the opening phases. 
I'd also try to completely avoid calculating when it wasn't my turn, to save energy. I'd get up and walk around to get my blood flowing and to avoid staring at a board for hours in the early rounds. Also consider that you have to calculate many irrelevant lines if you are trying to predict your opponents moves on their turn. Better to let them eliminate those irrelevant lines by picking something, and you can just calculate after that.
Based on following these methods and training about 3 hours each day, I broke through to 2200 in exactly one year, playing just 5 tournaments. I didn't lose a single game to anyone under 2200 USCF during that time, and split 5-5 with players at 2200-2300 (was 4-1 in my last 2 tournaments), drew a 2350, and I also beat an IM, lost to an IM, and blundered a won game against a GM (but at least it was an interesting game and he talked with me quite a bit afterwards). In my final 3 tournaments I closed out quite strongly in the last few rounds since I had plenty of energy, winning money in my last 3 tournaments (even winning an entire section). Beyond just training myself to be a good player, following these methods gave me a decent competitive edge over my competition and led to strong results. 

user-1: 
Don't think about the result. Don't think about anything. Just play chess.

Attributed to Josh Waitzkin in The Psychology of Competition training module in Ubisoft's Chessmaster program.
What does this mean to you?

Rating difference: When playing against lower rated players, a friend of mine said in a post-mortem that he deserved to win. But there are tremendous attacking and defensive resources in chess, implying that the result is very much uncertain at the outset. In short, a higher rated player doesn't deserve anything
Money/prizes: Do you need the money from the tournament? It is unlikely that you do. In this case, just see the prize as a nice bonus. It isn't yours yet, so don't think about spending it before it is handed over to you
Reaching 2850: I think this is unrealistic on your part. Carlsen is rated 2850. Dreaming about being World Champion and being the highest rated player of all time is another distracting goal. Don't think about how the game will affect your Elo.

In summary, when playing chess, just think about chess. The result is irrelevant. The rating difference is irrelevant. Try to stay in the moment.

user550: This won't be as comprehensive as some of the other answers, but some relevant points I've noticed from my other endeavors:

1) I can never seem to play against lower rated players. I am 2350 USCF and I have a higher win-rate against 2400s (around 75%) than even 2100-2200s (40-50%). 

Focusing on ratings aside (only you can say if the true issue lies there), often there is also a technical issue here as well. 
People can fall into a situation where they feel comfortable playing against opponents who play "correctly", but can't deal with people who play "incorrectly" or in an unexpected way. For example, high-rated player in chess might defend from an attack in a relatively orthodox manner, while a less experienced player might react by creating even more chaos and throwing pieces at you to throw you off-balance. 
The only real suggestion I can offer to counter this is to not just spend all of your study time looking at situation where the opponent defends perfectly but also consider the unorthodox replies that might emerge.

2) The last round has always been a struggle for me. A lot of the times I just collapse, especially if I need to win the last round for money or for a title.

This may also be due to exhaustion making it easier for you to lose concentration, and the potential outcomes providing a good distraction to draw your attention. Naturally, the way around this would be to maintain your energy levels as best you can during earlier rounds, eating/sleeping well and ensuring that you use time between rounds effectively to recharge your batteries (assuming, of course, that this is a weekend or similar short-scale tournament rather than a game-a-week affair).
This might have all been familiar to you already, but I hope it helps.

user10087: I have had this problem during the entire time I was playing official games. I don't know if I am entitled to answer your question, because you seem to be stronger than I was (2250 FIDE). Anyway, my way of combating this trouble has been efficient in the measure of what I deemed possible. My "trick" was to focus on the game, avoiding whenever possible to be distracted by the idiosyncrasies of my opponents (and mine), and try to play the "correct" move, being very cautious on verifying. I say the "correct" move, not the best move, because this would lead you into problems on time. Just try to play correct moves, as Smyslov has been said to say, I play 40 correct moves, try to do the same and we shall see. 
Of course, this does not mean you cannot take into account specific features or conditions occurring during the games. A bit of psychology is always necessary. But when you get nervous, just say to yourself, "Well no psychological auto-destruction, I just play right moves and that's all." This worked partially for me. Just try. It is purely mental, you have to adopt the right attitude, neutralizing any psychological negative interference. For this, of course, there is a price: you will also have to control and eliminate positive advantages during the game. By this I mean not getting overoptimistic when obtaining an advantage - whether psychological or real. If you can do this, you can become stronger. But that's only my opinion. 
Have a nice day!

user10339: The book "Mind Gym" helped my brother who's a professional gamer (online strategy games). It examines some of the ways that athletes can activate and harness their psychology to do better.
One thing in particular that helped me in competitive fields is to visualize in advance yourself winning: but not just winning, how you win. Visualize in color and detail how you're ready for everything, how you will deal with each challenge how you will persevere and keep focused throughout. 
If you've already won once in your head, you won't be surprised that things go well and you won't sabotage yourself.
Everybody has their hangups and this is purely psychological. But the psychological part is very powerful. It is actually a common problem for high performers that they'll do much worse against lower rated players/teams.
Practice more than anything can acclimate you to this. Practice against worse players. Practice against the players you want to be able to beat. Lesser quality players play markedly differently and it's possible that you've only mastered the high level kind of play and although you should have all the chess tools in house to beat them, you may be missing the right mentality and this might need some figuring out and some time.
There's an old saying in martial arts: "The best swordsman of the land shouldn't fear the second best swordsman: He should fear the worst swordsman".
(unpredictability can be a factor)

8672: <p>Having a correct mindset has been a frustrating endeavor in my chess career. I have some questions regarding how to get into a "correct mindset."</p>

<p>1) I can never seem to play against lower rated players. I am 2350 USCF and I have a higher win rate against 2400s (around 75%) than even 2100-2200s (40-50%). It's hard not to focus on the rating during my games, and it adds a lot of stress because I'm not expected to lose.</p>

<p>2) The last round has always been a struggle for me. A lot of the times I just collapse, especially if I need to win the last round for money or for a title. </p>

<p>3) I've lost against lower rated players so much that tournaments become stressful. This is mainly due to the fact that if I lose to a lower rated player in round 1, I am doomed to pair down the rest of the tournament. </p>

<p>I can probably play 500 points better if I could get rid of all this unnecessary stress. The real question is how to get rid of it. Trying to calm down is a paradox. Some of the best games I've played was when I got so absorbed by the position I forget about everything else.</p>

<p>I appreciate all advice. Thanks for reading this post. </p>
 10348: <p>@user3456... I think your answer suits more, although I am not in a position to conclude. Playing to win is actually riskier than playing for a draw. When I play someone with a lower rating, I tend to end up losing than win, but it gets more challenging when I play someone stronger. I go all out, and end up doing well.
.
To solve it in my own understanding, is to learn to be brutal. Show no mercy, to even a 1300. "Kill them all"</p>
 9627: <p>This worked for me when I was 2030 USCF and was attempting to climb my way to USCF master rating in 1 year. Psychologically I had 2 goals/methods:</p>

<p>1) Play every game based on the board, and try to play the best moves no matter how crazy or complicated they seemed (or how quiet and dry in some cases). Whether my opponent was 1600 or 2450 it shouldn't matter and I should play the same move regardless, since my focus wasn't to beat my opponent but to find the best moves to play. Playing guess the move on thousands of gm games, double checked with engine analysis, helped solidify this into a habit. Also telling myself again and again not to care about the result, but instead to try and have an entertaining game I can learn from.</p>

<p>2) I would always avoid looking at my opponents rating on the pairings, and would tell my friends to NEVER tell me the rating of who I'm playing against. Knowing this would only distract my attention away from the board and trying to find the best moves. If my opponent were Magnus I would still want to aggressively take advantage of anything that seemed to be a mistake, aka not give him the benefit of the doubt on complicated positions, and if my opponent was 1200 I'd still avoid playing aggressively if the position called for quiet moves.</p>

<p>Also as far as your endurance problems I would never eat anything unhealthy during a tournament, only proteins and complex carbohydrates religiously (mixed bean salad, and turkey sandwiches without sauces mainly). I would do my best to get 8 hours of sleep each night and have a light workout each morning if the hotel had an exercise room. Even though my normal lifestyle isn't nearly this good, I'd change my habits for the tournaments to be more competitive.</p>

<p>Another thing I'd attempt to do is get through my first 20 or so moves in under an hour. Even if I didn't know the opening super well I didn't want to waste my energy on the opening phases. </p>

<p>I'd also try to completely avoid calculating when it wasn't my turn, to save energy. I'd get up and walk around to get my blood flowing and to avoid staring at a board for hours in the early rounds. Also consider that you have to calculate many irrelevant lines if you are trying to predict your opponents moves on their turn. Better to let them eliminate those irrelevant lines by picking something, and you can just calculate after that.</p>

<p>Based on following these methods and training about 3 hours each day, I broke through to 2200 in exactly one year, playing just 5 tournaments. I didn't lose a single game to anyone under 2200 USCF during that time, and split 5-5 with players at 2200-2300 (was 4-1 in my last 2 tournaments), drew a 2350, and I also beat an IM, lost to an IM, and blundered a won game against a GM (but at least it was an interesting game and he talked with me quite a bit afterwards). In my final 3 tournaments I closed out quite strongly in the last few rounds since I had plenty of energy, winning money in my last 3 tournaments (even winning an entire section). Beyond just training myself to be a good player, following these methods gave me a decent competitive edge over my competition and led to strong results. </p>
 -1: <blockquote>
  <p>Don't think about the result. Don't think about anything. Just play chess.</p>
</blockquote>

<p>Attributed to Josh Waitzkin in <em>The Psychology of Competition</em> training module in Ubisoft's <em>Chessmaster</em> program.</p>

<p>What does this mean to you?</p>

<ol>
<li><strong>Rating difference</strong>: When playing against lower rated players, a friend of mine said in a post-mortem that he <em>deserved</em> to win. But there are tremendous attacking and defensive resources in chess, implying that the result is very much uncertain at the outset. In short, a higher rated player doesn't <em>deserve</em> anything</li>
<li><strong>Money/prizes</strong>: Do you <em>need</em> the money from the tournament? It is unlikely that you do. In this case, just see the prize as a nice bonus. It isn't yours yet, so don't think about spending it before it is handed over to you</li>
<li><strong>Reaching 2850</strong>: I think this is unrealistic on your part. Carlsen is rated 2850. Dreaming about being World Champion and being the highest rated player of all time is another distracting goal. Don't think about how the game will affect your Elo.</li>
</ol>

<p>In summary, when playing chess, just think about chess. The result is irrelevant. The rating difference is irrelevant. Try to stay in the moment.</p>
 550: <p>This won't be as comprehensive as some of the other answers, but some relevant points I've noticed from my other endeavors:</p>

<blockquote>
  <p>1) I can never seem to play against lower rated players. I am 2350 USCF and I have a higher win-rate against 2400s (around 75%) than even 2100-2200s (40-50%). </p>
</blockquote>

<p>Focusing on ratings aside (only you can say if the true issue lies there), often there is also a technical issue here as well. </p>

<p>People can fall into a situation where they feel comfortable playing against opponents who play "correctly", but can't deal with people who play "incorrectly" or in an unexpected way. For example, high-rated player in chess might defend from an attack in a relatively orthodox manner, while a less experienced player might react by creating even more chaos and throwing pieces at you to throw you off-balance. </p>

<p>The only real suggestion I can offer to counter this is to not just spend all of your study time looking at situation where the opponent defends perfectly but also consider the unorthodox replies that might emerge.</p>

<blockquote>
  <p>2) The last round has always been a struggle for me. A lot of the times I just collapse, especially if I need to win the last round for money or for a title.</p>
</blockquote>

<p>This may also be due to exhaustion making it easier for you to lose concentration, and the potential outcomes providing a good distraction to draw your attention. Naturally, the way around this would be to maintain your energy levels as best you can during earlier rounds, eating/sleeping well and ensuring that you use time between rounds effectively to recharge your batteries (assuming, of course, that this is a weekend or similar short-scale tournament rather than a game-a-week affair).</p>

<p>This might have all been familiar to you already, but I hope it helps.</p>
 10087: <p>I have had this problem during the entire time I was playing official games. I don't know if I am entitled to answer your question, because you seem to be stronger than I was (2250 FIDE). Anyway, my way of combating this trouble has been efficient in the measure of what I deemed possible. My "trick" was to focus on the game, avoiding whenever possible to be distracted by the idiosyncrasies of my opponents (and mine), and try to play the "correct" move, being very cautious on verifying. I say the "correct" move, not the best move, because this would lead you into problems on time. Just try to play correct moves, as Smyslov has been said to say, I play 40 correct moves, try to do the same and we shall see. </p>

<p>Of course, this does not mean you cannot take into account specific features or conditions occurring during the games. A bit of psychology is always necessary. But when you get nervous, just say to yourself, "Well no psychological auto-destruction, I just play right moves and that's all." This worked partially for me. Just try. It is purely mental, you have to adopt the right attitude, neutralizing any psychological negative interference. For this, of course, there is a price: you will also have to control and eliminate positive advantages during the game. By this I mean not getting overoptimistic when obtaining an advantage - whether psychological or real. If you can do this, you can become stronger. But that's only my opinion. </p>

<p>Have a nice day!</p>
 10339: <p>The book "Mind Gym" helped my brother who's a professional gamer (online strategy games). It examines some of the ways that athletes can activate and harness their psychology to do better.</p>

<p>One thing in particular that helped me in competitive fields is to visualize in advance yourself winning: but not just winning, how you win. Visualize in color and detail how you're ready for everything, how you will deal with each challenge how you will persevere and keep focused throughout. </p>

<p>If you've already won once in your head, you won't be surprised that things go well and you won't sabotage yourself.</p>

<p>Everybody has their hangups and this is purely psychological. But the psychological part is very powerful. It is actually a common problem for high performers that they'll do much worse against lower rated players/teams.</p>

<p>Practice more than anything can acclimate you to this. Practice against worse players. Practice against the players you want to be able to beat. Lesser quality players play markedly differently and it's possible that you've only mastered the high level kind of play and although you should have all the chess tools in house to beat them, you may be missing the right mentality and this might need some figuring out and some time.</p>

<p>There's an old saying in martial arts: "The best swordsman of the land shouldn't fear the second best swordsman: He should fear the worst swordsman".</p>

<p>(unpredictability can be a factor)</p>
