For local reference, I've made the round trip from great falls to Missoula a handful of times and it does great. I shoot for 75 mph and maintain it pretty well besides a couple of the longer climbs between sun prairie and Lincoln. I've never been the one holding up traffic on Roger's pass! I have a 2019 with the 3.73 gears, stock tires, and the diesel freak stage 2 tune. That trip is the one I've seen the worst fuel economy on, usually 22-23 mpg.