Only have 400 miles on mine. Have not driven it in temps over 15F which is a big factor. The trip home from the dealer I averaged 12.5 but half of the trip was into a wicked head wind and my scangage was showing 100HP just to maintain 65MPH, which is the same amount of drag towing our 5th. The next day an 80 mile ride showed 13.5mpg. Then, I realized the hubs were locked in from the dealer. Put them in the auto position and went for another ride of mixed highway/gravel/town and ended up at 14.2mpg. It was 10F for that ride. I remember with my old 6 liter GM the mileage tanked when it was cold and even saw single digits at times. With the larger driveline components, the SD/HD's are affected by cold more than the 1/2 tons.
Once it warms up outside, it should be able to get 16 highway and 13-14 mixed. I figure if the towing mileage is the same as my eco on 87e10(should be able to get 9) and the highway mileage goes from 21 down to 15, it's about $500 more per year with 35% towing and 10k miles per year. Not free but not too bad.
