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.
While conventional non-synthetic oil is recommended to be changed every 3,000 miles, you can typically go 5,000 7,500+ miles on synthetic without worry. And though synthetic is much more expensive, it's worth the extra cost for drivers that dont want to change their oil as frequently.