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.
Re: Low mileage oil change. On the newest car (2010) with about 70K miles on it, I use synthetic oil and change it at about 8K miles, which takes about 7 months as it's our long distance vehicle. The 2004, which my wife drives, is local use only and has right at 20K miles. It gets regular oil and is changed once a year at inspection time.