It's a '95 FZJ80 with the A343F, 93,000 miles. Recent tranny flush a few months ago. What happens is when I put it into reverse and there's a load, such as trying to back up a hill or over something, the engine revs, the rig doesn't move and then a noise that sounds like metal grinding or slippage in the transmission occures. It's never a problem on the street or normal backing up. Works perfectly the rest of the time. I've searched the threads and everything seems to come back to a TSB regarding some check valve or something on the 343F. Does anyone have any more details or the TSB itself that I could look at? Referring to this thread, this sounds like my problem: https://forum.ih8mud.com/showthread.php?t=19571&highlight=343 One question I have is, if this is the problem, can I retrofit whatever changes need to be made to the checkvalve, oil rings, etc and stop this problem or is now too late? And does the fix really require removal and tear down of the tranny. Some threads seems to indicate that only the valve body needs to be removed and that the tranny can remain on the vehicle. Finally, has anyone found that using 4L in reverses helps negate the problem at all? Thanks much.