I have an 03 F250 6.0 PSD, AT, with 8" lift and 36" tires. I get 15 mpg hwy @ 75 mph unloaded and 8 mpg pulling a 10k# trailer. I always towed 70- 75 mph so I slowed one trip to 60 mph to try and get better mileage and that didn't make a lick of difference. I then put a DR. Performance predator towing module on it for more power and hopefully better mileage, I got alot more power but about a 1/2 mpg worse mileage. I have the latest update from the dealer on my computer and I run high air pressure in my tires, I am just totally disgusted with the mileage and I can't understand how the mileage can vary so much on these trucks. It pisses me off enough to call bullshit on these guys claiming 20+ and 14-15 towing with a 6.0 psd, lift and tires like myself. I have tried everything to get respectable mileage out of this diesel and can't seem to do it. I will also mention that before I got my lift and tires I was disappointed with 16 mpg highway unloaded @ 75-80 mph.