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.
Oil changes are needed frequently to avoid this problem (ergo every 3,000 to 5,000 miles). The durability of synthetic oil at the same engine temperature makes it a better-performing product because synthetic still stays in liquid, usable form longer. This tolerance for temperature means the oil can stay in the engine and can last as much as 7,000 miles before changing. Most oil and car warranties will put the maximum length of mileage before a change at 7,500 for petroleum-based products (many cars are closer to 5,000 even with today's better engines). Given the heat-tolerance properties of synthetic oil, 7,500 miles is not an issue.