I just made a trip to Montana and back to PA with the Smarty set on three and towing a 7x14 two axle loaded with some furniture and our luggage low profile trailer, four people in the truck running 75 mph through most of the states west of here, my overhead said 18. 5 but my hand calc was 15. 6. Running at home empty I get 16 mpg consistantly around the backroads and 21 mpg on the highway at 65mph. Iam running 185x17 with 3:73 gears and auto transmission, I just turned 26,000 miles on the truck. My 04' didn't get good fuel milage untill it broke 28,000 miles and it was at 21 mpg highway.
A guy at a rest stop in Indiana pulling a flatbead gooseneck with an 06' Ferd was telling me he was getting 24 mpg empty and 18 pullin the trailer, I figured he was just trying to impress me!!!