Okay. Pulling a skid steer with my 6.4 butte to Helena for the weekend netted me 8.8 mpg. Same route with my work truck (7.3) netted me 5.8. Exact same trailer.
Ding Ding Ding... I live halfway between Helena and Clancy. I know that drive well. I got my 7K loaded travel trailer in Butte. That is a great drive for assessing MPG. For those of you that don't know, from Butte in a couple miles you go straight up to the top of "hill" from 5500 feet to about 6500 feet in three miles Then you cross a big "park" for miles and then into a windy, curvy valley (stream cut) with turns rated as low as 35 mph in a couple of places, then a short flat run, then to a small pass (Boulder Hill) and then pretty much a downhill run to Helena... I believe it is rated as a "scenic drive" in some publications...
I have been pleasantly surprised by my mileage on my 2500 Hemi doing about the same as you, close to 9 mpg, likely lighter load. You always gotta watch that predictable "wind gust" place as you go down the hill from Boulder Hill to Boulder... There's one place that always lets you know the relationship between your trailer and your tow vehicle and who controls whom... My 1500's with travel trailer always got blown around at that one spot, not so much for the 2500, much better planted compared to a 2021 1500... More than enough oomph for my needs. YMMV