GVs and hills just don't mix.
I think is is really a pain when you are on a hill and start sliding off. What do we have here anyway? Greesed tracks and ice covered hills?
Also, you ever see a truck convoy go up a hill? They haul ass, same speed up the hill, down the hill, on level ground. I think AI don't have to be mindfull of the terrain.
If the AI trucks can climb hills, the GVs should be able to also.
I was in the M8 offline, trying to kill a truck convoy. They got to the hill and left me stuck at the bottom.