clubchamp98
Journeyman Pro
your not getting blisters because your glove is taking all the friction.I don't think it is a grip issue as I never have a blister usually after a round.
I think its something to do with my thumbs probably bending back more at the joint than most and the joint being where I mainly grip the club when trying to have a straight thumb due to it curling back towards my head away from the shaft slightly.
it sounds like a grip problem .
Try a couple of range practice sessions without a glove and you will see the skin redden.
Or wear a glove (old one ) but cut the worn thumb out you will soon know if your grip is moving.