I'm at the opposite end of the spectrum from the above poster. 2015 F450 with a daily average weight of 12k lbs with my tools in it. Running 4:30 gears with a slightly taller than stock tire. I average 13 around town, 17 on the highway at 70+.
I reset my trip B meter when I bought the truck. It has been tracking fuel mileage since April 1st 2016. Including regens, all idle time, all towing, all city and highway driving, after 3102 gallons of fuel burned, it's reading 13.1mpg average.
I'm pretty happy with that for a truck this heavy, geared this steep, with this much power on tap.