We just returned from a 4400 km (2750 mile) trip pulling our 5.0 with our 2011 Frontier. We traveled from Calgary, down through Montana, Idaho, Oregon, up the coast to Washington, up to B.C., and back along highway 3 to Calgary. Whew!
We went up (and down) a LOT OF PASSES, and avoided interstates at all cost. If I did it right, there is an attached pic of our rig at the top of Lolo Pass in Idaho. We also pulled up the Kootenay (Salmo-Creston) pass, which is higher and steeper (5823 ft).
We never felt under powered, but we did not push it either. I just calculated the mileage for the trip -- we averaged 19.7 miles per imperial gallon (16.4 mpg US), which we are very happy with.
Does anyone else track their mileage?