This is a commonly asked question. Typically, most of the trucks that roll through my shop get 12 to 15 mpg. We have done extensive testing and found that a good high flow air filter and upgraded exhaust are beneficial for mileage concerns. On Fords, the super chips tuner seems to be the best bet. We have also found that at 150K to 200K miles the fuel injectors have worn on the mechanical end and justify replacement as a cheap solution, but will provide better mpg. Don’t forget compression; this also could be a factor in poor fuel mileage!