Before this big, bad pickup arrived, manufacturers largely used upgraded versions of their light-duty trucks to handle heavy-duty work. The 1999 Super Duty was a separate model line with its own style and hardware underneath.
You can run a conventional oil 5K miles but you should be able to run a synthetic oil 7500 to 10000 miles. Royal Purple API-licensed synthetic engine oils allow motorists to travel as many as 12,000 miles as the recommended oil change interval.
Synthetic Oil for cars (How many miles can you really go on it before changing it) I usually get Synthetic oil for my vehicle so that I don't have to change the oil every 3000-3500 miles. Now I go around 5500-6000 miles on Synthetic oil. However, I noticed as I went to the gas station that for Mobile Oil (synthetic) that it says you can drive your car for 1 year or 15,000 miles on it, whichever comes first.