Sunday night, I decided that I wanted to stop muscling the ball as much as I do, and also stop squeezing the ball. I made a conscious effort to let my arm swing be natural, and I noticed a huge improvement, with the only muscle I noticed being when I accelerated through the ball and my follow through. I also tried to stop squeezing the ball, but that did not go as well. I felt like I kept wanting to drop the ball if I didn't squeeze it. I switched to my smallest thumb insert to try to force myself to keep my hand relaxed, knowing that if I squeeze the ball, I will never get the ball off my hand. On my first ball attempts, I pulled most of my shots, and I did not get the ball off my hand cleanly, and my rev rate was reduced based on what it was with a larger thumb hole. I would attribute this to the thumb just being too small, but on my spare shots, the ball felt much more clean off my hand and my rev rate was back up. This happened every frame but the ninth frame. I was all spares except for a strike in the ninth frame, which was an unlucky strike. I was shooting for an all spare game, and messed up lol  anyway, what would cause the ball to be much cleaner on my spare shots than my first ball shots? any tips for trying to not squeeze the ball? My fit as far as span I assume is accurate, as I go to a very accomplished driller.

I have been through this as well.  It took experimenting with different thumb pitches. I have a fairly large span that started with 3/4 reverse. I now have a relaxed grip and swing, ending up with 1/4 reverse, magic carpet in back of hole, and two pieces of black tape in front. Grab a old ball and spend the summer experimenting with pitches and tape

i didnt use tape for many years. i guess i didnt know the difference
had 20+ honor scores over those 15 or so years

decided i wanted to get better, bowl on tougher patterns, etc
lead to lessons, better fundamentals, grip change and also learning how tape thumbhole.
i had never done it before.
thought process taught to me by a gold level coach - any flexing of the thumb towards the pad causes the knuckle or joint to get wider in the thumbhole, if you can keep the thumb straight and relaxed, theoretically, it will come off the same every time.
i use layering, 1 full piece and several half pieces placed on top of each other lower in the hole to basically almost have my thumbnail touching the back side of the hole
this took some doing to get it to feel right.
it doesnt mean i still dont want to grab it sometimes, but when its right, it comes off so nice.
if i can get the ball through the heads and get it to roll properly, there is a huge difference in my game and scores.
based on this experience and the coaching i have had, i think its a large overlooked part of the game. proper taping of your thumbhole
just my .02$ worth

I do all sorts of crazy stuff, I love the thin tape too, the 1/2" I think?  If use thinner prices the release is much better too.

For those curious, here is a link to tiered taping:

http://www.itbca.bowlingknowledge.info/index.php/2013-fall/95-tiered-taping-a-process-to--grip-pressure-and-improve-swing-release

You don't.  You use as little bevel as necessary.  Some hands require more than others.

Bevel is used to accommodate the shape of the thumb not to release the ball
Big difference between the two

For those curious, here is a link to tiered taping:

http://www.itbca.bowlingknowledge.info/index.php/2013-fall/95-tiered-taping-a-process-to--grip-pressure-and-improve-swing-release

I just found this a few weeks ago, and I like it....helps keep the thumb relaxed.

I'm a chronic sufferer of squeezing the ball.  I'm going to try this tiered tape method next practice session, and see how it goes.  Thank you for posting this!