Assuming you're a right handed player. It sounds stupid, but I might have figured out a huge reason why I tend to fade/slice so much. I've always had my right thumb running parallel to the shaft, instead of wrapping it around. It's just always felt natural that way, but when I wrap it around, it obviously closes the face a little bit.
I forced myself to hit balls yesterday with the new grip the entire time, and I've never hit so many straight balls in my life. This is probably all a no-brainer, but I'm excited that I might have figured out something that will make a big difference. Where's your right thumb?