So I have a 2000 tj with an ax-15. I know doesn’t make sense lol. As nv3500 or 3550 can’t remember which it is that comes stock in my tj is extremely expensive to rebuild for a 1/4 ton truck transmission when it went out last year I swapped an ax-15 out of a yj into my tj. It had an unknown number of miles on it as it had probably been in different Jeeps. Made some noises but just sounded like bearings that were old. One day not sure if I hit a bump or something but I was cruising in neutral getting off the highway and the transmission started making a light grinding sound almost as if I was trying to put it in gear without the clutch but it was in neutral. It wouldn’t allow me to go into gear either. Then it stopped and acted fine. The next day was on my way to work and felt it do the same thing so I took it home and parked it. I need to check the fluid but I just did a fluid change in it because it was leaking and wanted to add some stop leak. I didn’t notice a leak after the fact but am going to check the fluid this weekend regardless and try adding more to see if that helps. If anyone has had this problem before or has any insight on what it is some knowledge on the issue would be much appreciated.