In my opinion, as a newbie to TGM, 10-2-B is the only grip to use according to Mr. Kelly's teachings. It sounds to me as though your hand is moving during the swing causing this problem. Please post pics of your grip or go see someone who fully understands TGM. Moving the thumb to the aft side of the shaft was totally foreign to me until I started studying TGM through YODA, and now there is no other way to properly grip the golf club, again in my opinion.
Kevin
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I could be wrong. I have been before, and will be again.