One leg of a late September trip to Yellowstone two weeks ago, I averaged 22.987 MPG (24.0 displayed and 22.987 hand calc'd) over a 360.4 mile stretch, uphill. That was from Boise City, OK to Cheyenne, WY.
I was loaded, running BFG AT T/A KO's 265/70-17 @ 45 PSI @ 75 MPH using cruise when traffic allowed.
Now some will say "Oh, yeah I got 30 mpg for 6 miles out of my driveway". BFD, who cares, right? This was over 360 miles @ 75 mph. I was impressed. Yes, 75 was the speed limit. It felt slow compared to the 80 mph limits North and West of Cheyenne.
My lifetime average with this same setup is 19.402 mpg actual hand calculated. Mostly in town mixed miles.