Overall the trip from Denver to my house, near Madison, was 12.6mpg.
The first 100 or so miles were in snowstorm so 45-55mph and EVIC said 13.7mpg. The rest was on dry roads, I-80, and cruise was set at 75mph most of the way.
It did use IMO, a lot of DEF fluid. Apparently it’s a 5 gallon DEF tank and we used about 1.5 tanks. That’s for the whole round trip, WI to Denver unloaded, the Denver back to WI with trailer.
The 2500 we used to use was a 6.6 Duramax and would usually be in the 11-12mpg range towing the same trailer. It didnt use any DEF though, that stuff must have rusted and fell off somewhere on the highway….haha