Yoda suggested that I bring my problem to this forum.
My fatal flaw when I apply TGM principles in search of a better move is that my left wrist arches, opening the clubface and producing a weak glancing blow to the ball.
I have played reasonably well for years coiling and releasing my big muscles with soft arms and passive hands. At the top, my left wrist was slightly cupped and when I fired through with my right shoulder and lat, the wrist would flatten through impact then turn over as my body released.
Now when I consciously push PP1 against the left thumb, the left wrist arches as the right wrist bends. The only way I have found to stop this is to set up with a strong (turned) left hand grip. But then I get into a blocked position with the left hand and arm wanting to come up rather than down and around.
I cannot for the life of me get a feel that gets the left wrist flat level and vertical through impact while pushing with the right hand and elbow.