I know this has been talked about a lot, but I want to put this out there in case anyone needed more convincing. My TJ has an NV3550 trans and if it is filled with synchromesh, it is very very difficult to shift. Feels super gritty and the shift lever gets caught up and stuck in different positions. This is regardless of how many times it is drained and refilled, so I know that dirty fluid is not the problem. Then if I drain and fill with Redline MTL, the shifter instantly and completely feels like one from a brand new vehicle. When I used to read posts about it, I thought people just had brand loyalty to redline, and that the difference would be imperceptible if anything. Well I was completely wrong. Maybe synchromesh is fine with a younger transmission, but if you have any trouble shifting at all with an NV3550, just drain and refill with MTL. It is very expensive unfortunately, but if you think about how it makes your trans feel brand new, then it is more than worth the cost.