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.
If you are using a quality motor oil, changing it at 3-4000 miles is a waste of money. That is, of course is dependant upon the items mentioned above. A synthetic fluid should be good for 10K easily, providing the items mentioned above are good. The key is Filtration, Filtration, Filtration