My cousin in Oklahoma has the 3500 version of the 1996 dodge ram. I have the 2500 5-speed.
He was having the same problem (mine backed off 3 times after a rebuild). My mechanic resorted to welding the nut on the shaft. His mechanic came up with the best by far solution. They removed the shaft and took it to a machinist and had it re-threaded with....... a rightey loosey and lefty tighty for a left hand nut. Never had a problem since even after a second rebuild @ 300,000.

 

i have had my nv4500 rebuilt top to bottom new parts at the local shop, they also installed the latest 5th gear retainer lock nut. bad news is 1700 miles later i lost 5th gear and i don't lug fifth, i don't know why lugging it changes but i try not to. sooo the shop then put a new 5th gear a lock nut on, but i also have had that retainer installed, works great have not had a problem with it yet and ive put 5k hard miles on it so far, i recomend it thats just my 2 cents

 

I put the updated nut much thicker and two brass set screws 10k+ still on there 5k towing STILL ON THERE

 

Does no-one take a center-punch and stake the thread in 2-3 places after getting to proper torque? Seems like that would be much less intrusive than welding, and you'd still be able to torque it off with a wrench if needed. Or is the reversing aggressive enough to run over a dimple?

 

To the best of my knowledge, the dimple isn't good enough for holding it.

 

what about welding the nut to the gear instead to the shaft?

 

That's actually not a bad thought ... .. never been in one but if its close enough to the gear I would say go for it ..... either way your gonna have to file or grind that bad boy off when u need to change it ...