My mileage started out looking really good. I got 21.7 hand-calculated driving 65 on cruise control at 3000 miles. I thought this was awesome. But subsequent checks (hand calculated) kept showing the mpg dropping with more accumulated miles. Mileage had dropped to 18.4 at 65 mph on cruise at 10500 miles and using Cetane booster also. I just changed tires from 265/70/17 stock to 285/70/17 running 80 psi. These tires are 1 inch taller and 3/4 inch wider. Not a huge increase in size at all. However I lost 5.5 mpg at 65!!! Evidently it really does make a difference when the computer is not updated as to a change in tire size. I am going to get that done tomorrow. I am seriously thinking about getting rid of this truck. With diesel prices ramping up with no end in sight and my mileage falling off a cliff, I think I will lose this truck before it gets any more miles on it. I would definitely not recommend anyone buy one of these new ford trucks.