Let me preface this by saying I am NOT a mountain person. I have spent almost all my life on flat coastal plain, river swamps, and a few years of it in the Amazon rain forest. All really flat by most people's standards.
30 some years ago, I spent a few weeks doing some fertilizer spreading for a start-up dealer in the mountains near Rockmart Ga. I had my first 2375 IH, 270hp L10 Cummins, 9 speed. I had NEVER driven a truck in the mountains before. I had to go down a very steep, (even by local's standards) 2 lane rural road that had a lot of traffic due to a new development. It also had a nice 90 near the bottom with a drop off. I was loaded to the gills and had a tag trailer with a farm tractor/loader. I nervously crept down and did what I had to do, and started back up right at evening rush hour. It was so steep I couldn't make 4th gear even though I was now empty and just towing the tractor.
I settled back to just chug up the hill at 15 mph, and looked over at the local woman who was riding with me as my guide. I wasn't worried much going up, but she had a white knuckle grip and was staring intently in the mirror! I asked what was bothering her and she said "we must have a hundred cars piled up behind us". I said they would just have to follow us all the way up and I would pull over at the top. She said, "But, if it gets too steep, won't the trailer come off?!"