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.
Mobil 1 Extended Performance synthetic oil is recommended for oil change intervals up to 15,000 miles or one year, whichever occurs first. However, if your vehicle manufacturer recommends an oil change interval beyond 15,000 miles and Mobil 1 Extended Performance meets the performance level specified, you can be assured that Mobil 1 Extended Performance will go the distance.