As I'm reading this thread from April onward to the present, I keep wanting to say, that possibly not only were your span and your forward/reverse pitches off, but very possibly your left/right pitch was also off. Many times people assume they need no left or right pitch in their thumb, but few people need 0 left/right.
Make sure the left/right pitch, as well as the forward reverse is right for your hand. The fact that 1/8" left pitch started to feel better, makes me think that you might really want to try 1/4" left pitch to see how comfortable that is.
Have you ever gone to a better pro shop, one noted for its ability to do the grip right? That may be THE one most important thing you do in bowling. Just like "you can't outbowl a bad ball reaction," you also can't outbowl a bad grip. Almost every aspect has to be right for most people; a few rare people with a lot of strength AND flexibility can get away with more errors in the fitting. Most of us can't.