I just finished a 3200 mile trip around the west. Most at or near 5000'. Towed 9500 lbs. 2018 Ram 2500 6.4, 4.10.
I never hand calc'd but the trip meter said 9.6 mpg. That include probably 250 miles of non towing.
Lots of 2nd, 3rd, 4th gear stuff in the mountains and two long days running 60-65 mph in 5th. Some tailwinds and headwinds. Flat and mountains. Pretty much covered all conditons. Even one run up and over Teton Pass in WY. 1st gear wound out tight at 4800 rpms for part of it.
I just figure 9 mpg as my base for distance per tank purposes. The EVIC is probably off as that seems to be the norm. I know one thing for sure, my truck loves gas stations.