I'm in the same boat as the OP.
Currently I run a 2012 F350 XL Reg Cab 6.2 gas 4x4 w/ 3.73's and e-diff
Towing my 6x10 enclosed trailer with Walker, push mower, blowers etc I get 11-12mpg's. Lots of stopping and starting. No highway driving.
Empty and w/o trailer I get around 15mpg's
Average range on a full tank: 365miles Towing, Around 400 Empty
Winter fuel is here and I have seen MPG's drop by a MPG or two.
I'm somewhat ocd and I do the math every fill up.
Also average around 14-17hrs per fill up.
I love the power, this truck is strong. I fill up once a week.
Now I'm looking for a 'cheap' diesel dump for my crew to drive.
I don't want to pay the guys to stop at a gas station every other day.
Finding the right truck is hard, I looked at used trucks for 2 years. All I saw was crap and didn't want to waste my money. I've got a 5yr warranty to help me sleep at night.