I don't know what else to suggest. The locker is the strongest thing out there, and probably the best for a car that is heavily drag raced. But as you have noticed, they can be harsh. I think the Truetrac is the best limited slip out right now for the 9" rears. My last diff was an Auburn pro series. It worked great at first, but wore out fairly quickly. The Truetrac hooks up just as well, doesn't seem to wear out, and is smoother on the street. If 9 second cars are running them, I guess they can hold up. Good luck,
Andy