I'll give my experiences so far, currently at 13k miles on mine. It's a 2021 F250, with the 4.30 gears. Very well equipped Lariat, 10k GVWR, payload is 2700 lbs. 2.5" lift with 37" tires.

I live in Northern Utah, anytime we go camping, fishing, or hunting, we have to pass over at least one mountain range. Empty freeway mileage ranges from 14-16 depending mostly on speed, hills don't seem to reduce mileage as much as I would have expected, when it's empty. Towing our 10k 5th wheel, with a 3k lb side by side behind that, I get 8 ish MPG. For reference, my Dad has a 2016 with a 6.7 Powerstroke, and he gets 10 MPG pulling a similar setup.



[Linked Image from i.imgur.com]