The pickup manufacturers get in these races with each other and throw practicality out the door. Our 2011 2500hd just has turned 2 with 56000 on it its a 6.0 that gets 8-9 loaded 10-12 empty it is 4x4 x-cab. 2 mos ago we bought '13 F250 4x4 x-cab with a 6.2 gas at 6000 miles the milage is the except on the road it will get 12-13 both are 3.73 and almost identical it replaces 04 F250 4x4 x-cab 5.4 pretty much same gears and mpg. This truck has 196000 miles we just sold Dodge 3500 4x4 Cummins 96 model had 11 ft flat it got 10-12 empty and 16 loaded. We still also have two GMC 3500's a 7.4 and 8.1. Just can't make the added expense for the diesel work.
We can't trailer as cheap as we can use the mediums and when they pull our 18' flat they pull nearly free. If you don't think I know which brand of truck runs the cheapest try me.