I bought a 2002 f-250 ec, lb, 4x4. I am getting around 15.5 mpg with a canopy and 500 pounds of tools in the back. The truck is bone stock with 68,000 miles on it. So far I have changed the oil plus filter, fuel filter and air filter. What should I do next to help with the mpg's and to keep the truck running great.
As stated, your mileage seems right. Make sure your brakes are in good working order and your tire pressure is right.
Driving habits and overall mechanical condition of the truck are the biggest two contributing factors of fuel mileage. If both of those are in check, then you should be getting the best mileage possible.