My experience form trips to Colorado with my Tiffin Allegro was that I always got better gas milage in the mountains than I did on the open highways getting to Colorado. At the time most of the posted speeds were 55 or 65 and I did the speed limit. except in the mountains, I slowed down first because of the twisty roads. I took the curves at the speeds posted on the yellow recommended speed signs and second because the coach simply could not get back to the posted limit before the next curve, so I stopped trying. The other reason was that I spent a lot of time coasting downhill in second gear to keep my speed under control. I know that going uphill I was probably getting maybe 2mpg but going down the engine did little more than idle. In Colorado for every up there is an equal down, apparently the down segment fuel usage more than compensated for the heavy use going up. I if remember correctly I once managed 14mpg compared to 8mpg on the open highway. Also, as far could tell towing a 3900# Jeep Grand Cherokee did not make any noticeable difference in my fuel economy. If I recall correctly the sweet spot ofr the best overall fuel economy is somewhere around 45 - 50 MPH. I think my average speed in the mountains was about 40 MPH.
2018 Thor ACE 30.3
Towing 2020 Jeep Gladiator
Former 1996 28' Tiffin Allegro owner