Hay,
in response to your question about anybody flying glow in IMAC, I do in the NC devision.
I fly a GP .46 300s. and had the same problems, but only when I floped hammerheads. My tank is not on the CG, and i don't run a pump, and I have won a few contests. I just tuned my engine to have best performence, and I do well. I think your problem is that you are snapping to hard, try it with only rudder and elevator.