It is frightening that we are sold large heavy road equipment that contains systems for safe driving on grades and we are not educated in how to use them. Of course that assumes that the salesman or delivery individual actually knew how to use the equipment. Lack of knowledge about descending steep grades will kill RVers and innocent victims in their path. It happens! Shifting up to "protect the engine" could result in loss of control of the vehicle unless brakes are firmly applied and then what happens to the brakes. They fade away.
Tow/Haul Ford and Grade Brake GM both provide a margin of safety initiating the downshift that a knowledgeable driver could take on his/her own. Understanding that the higher revs are helpful and that the tach is the source of information about engine speed and not hearing alone is vital. My old 8.1 L would howl all the way up a long grade at 4,500 RPM in 1st or second and just say thanks for the exercise at the crest. I must not have been to bad as it was still running smoothly when I sold it with over 105,000 miles on it. Likewise on long descents the Allison would never let the engine over rev it just upshifted and then I had to hit the brakes to get under my target speed and start the cycle over.
They don't teach you this when they hand you the keys and say have great day. They ought to.
Rant mode off