With our 40' MH we have driven 34 (Trail Ridge Rd.) through Rocky Mtn. Nat'l Park. Yes, it's steep and I would highly recommend you start out early morning before the big rush. Many RVers drive it. It depends on your mountain experience.
We've also taken 40 across Colorado into Vernal, Utah. No problem there. If you want to continue from Vernal to Flaming Gorge northward, Hwy 191 also has a steep section but again, we've done it as have other RVers.
If you have the 'Mountain Directory for RVers & Truckers' these roads will give you a good description.
Full-timed for 16 Years
. . . Back in S&B Again
Traveled in a 2004 Newmar Dutch Star 40' Diesel