I have a 06 F250 crew long box 16-18 empty and 13-16 with a 20′ enclosed work trailer. I was a dihard chevy man owning 3 6.5 diesels and running them to 175,000. 2 sucked on milage and repairs and the other buller proof. Last truck was F250 crew shortbox after 100,000 and chip I could get 20 empty and 17 loaded. Speed and tire size make a huge difference if you are looking for milage. For me I wanted a truck that I could beat on without worrying about maintance issues. I found the Superduty to be tougher, not necessarly better they are both great trucks. When your spending in the mid. $40,000 for a truck I don’t think your are really conserned about 3-4 miles to the gallon. A truck isn’t meant to be for economy, work, play and pay the price when you fill up. Only $116.00 per fill with the larger tank, yes it does add up when you fill every week.
Good luck truck shopping.
Brian