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.
Especially since it's a good synthetic type. Personally, I change my oil in both of my cars every 3 months, because I don't drive 3000 miles in that much time. It takes me more like 5 or 6 months to go 3000 miles, so I change it 3 months.