Did some more light towing with my truck this weekend again and found that I can pull my two place clamshell snowmobile trailer in 6th gear without much fuss at all, at 75 mph and getting 12.5-13 mpg. Granted, the whole setup might only weigh 2200ish lbs rolling down the road but the trailer cap turns this thing into a huge windblock when you're rolling down the highway. Plus, northern lower Michigan is no slouch for decent grades and hilly terrain so although it did downshift to 5th a couple of times, the trans temp never scowered over 125 degrees the whole pull (100 ish miles one way).
Again, very impressive seeing as how a friend of mine pulled a very similar trailer for a while (until he upgraded to bigger), with his '08 HD 6l and had to leave the 6 speed in 5th gear and got no better than 9 mpg rolling the same speed.
Same goes for how my '98 use to pull this same trailer. While I would never think of trying to pull this trailer in 4th gear in the truck, it would pull it without issue or downshift, in 3rd gear all day long however, at that speed and engine rpm, 10 mpg was the best you were getting, period. 9, if you were bucking a headwind the whole way.
Just more reason to love my purchase more and more.