Well, I wouldn't say it's crap. It can have a few problems here and there without being crap.
The retaining nut backing off is actually a common problem among NV4500s, so chalk that one up to poor design, and expect that it could happen to any NV4500.
Maybe you left the following details out because they weren't a factor in any of these cases (and I'm not trying to insult your family's or friend's intelligence), but I'd be curious to know if the lube levels were up, and if everyone, including the previous owners, used the correct synthetic lube. Was the Cummins chipped? There's so many different reasons why a tranny can go out and I'd have to know more before I would say that the NV4500 is a bad tranny.