I went up a place called the Sonora pass in California. They did not advise that it was a 28% grade 1/2 way up. With a 40' 5th wheel I could not turn around when I found out so up I went. It all depends on your truck and how many switchbacks it has. I have a f350 dully and surprisingly enough I had no trouble going up. It was 7 miles that my nerves to a beating on but it can be done with the correct truck.
A situation like this is where torque would be your best friend. If I had a NA gas engine, I'd want a seriously low first gear so I could rev without moving very fast. So, what type of gearing do these things have???