I have this problem but have it solved with tape. The problem I was having was with the tape. I have been using the brand "bowlers tape" Black to snug up the thumb. Well with this tape I could snug up the thumb perfect but when I would release the ball I would hang. Basically the black tape was not slick enough.
So I started to look into getting the "slick tape" that I have read about. Well this past Sunday at league I went into the pro shop and the guy pointed me too Ebonites brand of black tape called " Ultra-Grip Black tape 1". This tape is thicker than the bowlers tape brand. Next, this black tape is SLICK. The tape almost feels like thin pieces of plastic. Well I put it in the thumb and got a perfect tight fit. I go to release the ball and I come out of it perfect. This stuff is awesome. I will be buying a case of this tape. I wish I would have tried this before.
So give this tape a try and you wont regret it.