OK, so I was at my drivetrain shop getting a seal in my transfer case input...

Was talking to the guy about the 5th gear nut failure on the NV4500's - and he showed me the updated nut and such... turns out it was a lengthy discussion and we both felt that my truck was fine.

So I leave and while cruising down 80, guess what?

I turned it right around and back in the shop.

I guess it was sooner than expected because 5th gear is chewed up a little - had to buy a new gear.

Got the nut with the brass hickies on it and set screws - gonna loc-tite it as well.

 

Bummer
There was a good read a little while ago on the 5th gear syndrom and the "cause and true fix" according to the experts. If I find the post I will put up the link.