My drilling change was similar to what J_w73 described. Shortening/relaxing of the span. My previous span, though it felt normal to me, was so wide that I did not insert my fingers all the way to the first joint.
Also... the pitch of the thumb was changed slightly, but not certain of that. Other thing is, the thumbholes (on the new drilling) are just about perfect now, requiring only 1 or 0 pieces of tape in the summer, and 2 or 3 in the winter. BUT.... I might need a smidgen more beveling, and have resisted because in the past it's been extremely easy for the driller (any driller) to go from an excellent minor adjustment to too much bevel. With too much bevel, I tend to lose the ball or feel as if I'm going to, which causes me to squeeze and we all know that doesn't promote good bowling.
So... my release probably isn't as clean sometimes as it could be, and I may need to grit my teeth and see if I can get the thumhole's bevel increased just a tad. Am resisting, though, at least till the fall when my thumb will shrink somewhat.