Good write up. I had the problem of shooting left or low, left. I found that if I get a good strong grip with my strong hand, I don't have the problem of my fingers tightening on the gun when I pull the trigger which pulls the gun left.
Test: Hold your strong hand out in front of you (empty) and make a loose fist. There should be at least a couple of inches between your fingers and the palm of your hand. Point your trigger finger out straight. Now pull the trigger finger in like you're pulling a trigger. Do the other fingers want to close? It's an automatic reaction but if your fingers are already tight, the gun shouldn't move.
I also found that if I take my weak hand and wrap it firmly around my strong hand with my thumb just under the slide and put pressure towards my strong hand, it helps prevent the leftward movement. And, I can actually feel when I'm not pulling the trigger correctly and in anticipating the shot. It's fascinating all the dynamics that go on when shooting.