We have a 42' long 4 horse trailer with living quarters. Dry and empty the trailer weighs nearly 14,000 pounds. Fully loaded the trailer weighs over 20,000. We ran out to the Clear Springs Rodeo this summer. Driving into a head wind, mpg ran a bit over 6, on the return trip with a slight tail wind we averaged over 8 mpg. Empty the truck averages a bit over 10 mpg. Pulling a trailer of this size - that isn't too bad. Truck drives great, pulls our trailer with ease (we can keep up with cars pulling away from stop lights). It rides much smoother then our previous F350 due to the wider stance, I believe. Great Truck!
I am happy with the truck so far. I read a lot of reviews on the 08 truck that were not too good. If people want good fuel mileage, buy something else or modify this truck. Mine was getting around 10 mpg but after a few modifications it is now averaging around 15 and has a ridiculous amount of power. Spent about $2500 on the truck to get it there and it was well worth it. If something does break I'm sure the warranty won't cover it if the mods caused the breakage, but that's my own fault. I have owned 3 Duramax trucks, 2 Cummins, 1 7.3 Powerstroke and this one. This is by far my favorite diesel!