My 97 XJ has a 231 t-case. It has an aftermarket output shaft to eliminate the slip yoke and I put a fresh chain in at the same time 50,000 miles ago. The case has 245K on it. Lately I have been getting what feels like a slip when accelerating heavily in low gear at low speed. It isn't a fast stripping sound but you can sort feel it and easily hear it, I guess it isn't so much a slip as it is a noise and feel. I thought my rear locker might be slipping but I did an assorment of burnouts one tire on dirt one tire on pavement(did it for both sides) as well as a good old smokey pavement burnout lol, no signs that the locker is giving up at all. Its been like 12 years since I was last inside the t-case so I can't picture what is in there to maybe make this noise?