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.
For example, some vehicle manufacturers advise an oil change interval of 7500 miles when synthetic oil is used; some others recommend an even longer interval. Oil Viscosity. Engines are designed to operate with oil of a certain viscosity.