man, ur form and shape pretty close to me, and i can tell we have a lot of things in common.
the problem of letting it go instead of grabbing it or hitting on the ball too much.
this is what im currently doing:
1: back to no finger insert, that would be the first thing to prevent myself from hitting on the ball too much
2: i slow down during downswing, to get the right feel, i even go from gutter to gutter just to get the feel
3: i stopped landing the ball like a plane, instead i intentionally force the ball to fall off my hand, if u cant imagine that, watch Billy O on brunswick videos. I actually saw him doing it and it made a big difference after trying it.
few things i dont suggest u to change, slow down ur feet and swing straighter. ur footwork should be relative to the condition u r facing, walk faster if u wanna throw it faster and let ur arm coordinate with ur feet.
ohh and about sucking... cmon lefty, we all know its easier on ur side
When a house bowler misses the mark, misses the break point and strike, for many ppl its called a wallshot. When a pro does that its call adjustment
When a house bowler gets his finger stuck in the ball and fall on the lanes, for many ppl its called lame bowler. When a pro does that its called the Machuga flop! ha i like this one.