In 2003 I pulled a 30 foot Fleetwood travel trailer all over the Rockies with a Dodge Ram 2500 gasser. It was not easy but not impossible. I had numerous occasions of overheating. In most cases I could find a spot to pull over and wait for the engine to cool. A few times, maybe 3 or 4 over a ten week period, I could find no shoulder and had to climb to the top. I downshifted, getting the rpms up, and went as slow as I could but still keep momentum going, and prayed all the way to the top.
If I had it to do over again, I would still do it. But there was risk involved. the big difference to back east is not the steepness, but the length of the inclines. I have since added a transmission cooler, but have given the van and trailer to my son and upgraded to an MH.