I've done all that. Ok, here's what I've been able to figure out. What I think is happening is that the sear is tripping on the trigger block and not on the small block that it is supposed to trip on. If you look at the pictures below, you can see that the top of the trigger block is worn near the back. And after fiddling with it disassembled, I can tell that based on the position of the hammer during the pump return, that it is shooting right when it reaches the trigger block where it is worn.