You have to realize that it's a bad idea to hit hard (lower percentage) shots to an opponent if they have a consistent backhand and you're not moving them.
1. They don't have to move.
2. They are more consistent than you and you're going to make an error first.
The only time it's really worth going for a shot with a lot of pace is if you want to exploit how much time your opponent will have to react. So, if you're trying to hit it past them into a small area of open court, it would make sense. However, if they're in position for your shot anyway, you're better off exploiting depth, height, or angle unless you have an absolutely devastating amount of pace (which you most likely don't at 3.5).
So instead of pummeling his backhand next time, try a loopy ball up high to his backhand. It's a safe shot, so worse case scenario is that he hit back a moderate pace shot and the rally is still neutral. Best case scenario, he misses or gives you a short ball to put away. Or you could try hitting a medium pace shot to hit backhand, then hit him a slice, hit him a high ball, etc, until it screws him up and he misses.
Think of Federer vs Djokovic's backhand. It's super solid and he's not going to hit through him, so he mixes it up or tries to run around the backhand and take it up the line once he gets Djokovic out of position.