It doesn't matter if you have a gas or a diesel RV, you drive any steep mountain pass with caution. You use caution coming down so as to keep your brakes cool and caution going up so as to keep your engine and transmission cool.
Along the side of most mountain passes you will see the things called RUNAWAY truck ramps. They are not called Runaway RV ramps. This is because, from experience, the highway design engineers know that there will be many large diesel trucks that experience brake failure. Diesel RV's are not immune to brake failure.
Use common sense and don't be in a hurry to get to the top, or bottom, of any steep highway and things will work out fine.