With the 5th wheel, if you can get it up there, then you may need to manuever, disconnect and reposition the angle of the truck, reconnect. Repeat as necessary.
Someone else mentioned about clearance. Make sure as you start up and hill, and you crest it, that you don't hit the top of the bed with the trailer.
I have a short section of steep drive with a curve; I have to watch how I approach that area. Starting up the hill, the front of the 5th wheel gets close to the bed. As I crest the hill, the top of the taligate gets real close to the trailer body. Never actually bumped, but I do approach that part of the drive carefully.