I don't have the answer, but I can tell you the exact same thing used to happen to me. I can remember playing "Long Train Running" and the pick would start shifting in my grip and rotating and I would start praying I wouldn't lose it! There were times I was playing with the back of the pick before I reached a part in the song where I could shift it back.

I never did anything to resolve it...it just resolved itself. It didn't take long to resolve either as I recall.

I didn't change the pick I was using, though you can find picks that are more grippy. I've read where players would score the sides of the pick with the knife to create grooves to make it more grippy.

You are right though that you don't want to become too stiff or rigid by tightening your grip.


Perhaps not the answer you were looking for...but all it may take is to continue to practice and your fingers will figure out on their own what they need to do to keep the pick in hand.