theres an old saying, if a man is convinced he is going to die today, he will probably find a way to make it happen.
From reading your posts and attitudes on this board, it is my belief you are very self defeating, your worry about doing the right thing, you wish oh please make this shot instead of having confidence in doing it.
To perform to the absolute best you can, you must have confidence in yourself that you can do what is required to be done, and right now you have none. You defeat yourself before you even step onto a lane saying well i can't bowl because this happens, or i cant throw a good shot because i bend my thumb or whatever.
Don't sweat the small stuff, believe in yourself, as you said in your earlier post you have proven before you can accell at this game, and according to your profile you have only done it three years and have accomplished alot, many of us including myself have been bowling upwards of 20 years, some even longer than that. Of course we have better muscle memory and better coordination or better feel for the game, we simply have done it for so long it is a very natural thing, much like learning to write, or riding a bicycle. I've bowled since i was 2 years old, i've done it so much it seems like a very natural motion. For you it seems you need to force the issue, but if you have mechanical problems now, you are lucky because you only have 3 yrs of muscle memory to correct, when someone like me has a problem, i might have been doing it for 10 years, it is much much more difficult to correct.
My suggestion is this. Do what we said physically practice wise, work out your wrists if you have to or whatever, get a wristband, anything.
Mentally, remind yourself on the way to the lanes the times you have been successful in this game, concentrate on how your mechanics felt, think of what it looks like, or felt like. Go into the lanes or league not thinking or hoping to shoot well that night. Go in being absolutely positive you are going to shoot well. If you get tapped, or a bad break, forget about it and keep this attitude. Confidence is a huge factor, you may have a solid phyiscal game, but mentally as you said you only have 3 years of mental makeup, you need to learn some of the basic mental principals which make good bowlers great.
Hope this helps, if you have any questions or need more detailed info respond in this thread or message me.
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am i still considered a lefty, i never get to play the left side of the lane