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.
1 You could change the oil to a fully synthetic type if you are not using such oil already. Synthetic oils have a lower volatility so this can also have an impact on the oil consumption.  Change your driving-style to stay between 2-2.5k RPM most of the time.