I have a 1999 F150, 4wd,5.4 auto,std cab, long box. I get 10-11 mpg pulling my 27 ft travel trailer with 1-3 motorcycles in the back, running 60-65. 18mpg empty at Interstate speeds. What I did was; installed LT tires and ran them at 65psi, totally ventilated the airbox and installed a K&N filter, straight thru muffler, installed a Diablo Revolution chip and had it tuned for max mileage, and removed the clutch fan and installed a electric fan in the stock shroud. The fan was the biggest gain. I also always run synthetic oil. Just food for thought. I think the biggest problem for improving my mileage is aerodynamics, I have thought of building a air diffuser on the back of the travel trailer to break up the low pressure area behind the flat back of the trailer. And maybe air dams at the front of the truck and trailer.