While you are looking for other options, I would suggest changing the oil and maybe overfilling 1 quart too. Just to make sure there is oil in it and its fresh.

 

Advance Adapters sells a kit to swap the getrag for an nv4500. It is a little spendy, but you won't have to source a lot of extra parts.

http://www.nv4500.com/product_info.p...ducts_id/24294

 

Same thing happened to me . I cut a hole in the floor a little larger than the top cover and removed the top plate and found that the roll pins were comming out and one dropped to the bottom of the trans where I was lucky enought to find with a long magnet tool . I cleaned the holes on the shifting forks with brake cleaner and lock tighted them in . Been two years no problem so far daily driver ( I was driving hard in 5th gear on a straight away . I just over heated the trans even with 5 quarts 5/30 mobile 1 . Got it to 110 with 307 gears and when I slowed down and reshifted at the stop sign my shifter was sloppy and the gears ground when I was able to find a gear . Next morning it shifted good enough to get it home with no problem ...Weard but it happened to me

 

I would fix the Getrag many times before I would swap in an NV4500.

The Getrag is the better transmission.

I know many Getrags around my area, most being original owner trucks, and very few of them have ever had any real problems with them.

On the other hand, just about every NV4500 truck around here has had major transmission break-down more than once, and not all the break-downs are related to the infamous 5th gear nut.