Stock, a Th350 will loose prime anywhere beyond what would be considered "moderate angles". In fact, it will be able to handle driver's side up less than passenger's side up by a few degrees due to offset pick-up.
However, with a "+3" pan and offset pick-up, I can go nearly onto the side before "loosing prime". This is basically the same thing Rob and most of the rock guys do to get more angle.
I also run about 1 qt over full. Any more than that and it blows it out.