1993 Xj 4.0L AW4 Reverse noise

This is my first post on this forum. I recently bought another Jeep, a 1993 Jeep Xj with a 4.0L, AW4 and a NP242. I bought it with an issue that Ive managed to fix but I found out another issue with the Jeep. When I put the vehicle in reverse its fine until about 1000-1200 rpm and once it makes it upto that rpm range I hear a clunking noise or a knocking noise and occasionally it will cause the engine to stall out if you give it more throttle. Its fine in every other gear, shifts fine. The fluid level looks to be over the full line, but the previous owner said it was happening before he over filled it. I checked the search and couldn't find anything related, managed to find a webpage with links to diagnosing the AW4 and the pages wouldn't load so I assume the file was removed.

Any ideas what to check? I tried to upload a video but my camera/computer sucks and it wont show me the video file on my computer.