I believe the 5th gear issue is due to the nut vibrating off. I think a lot of that falls on the 12 valve working so well at such low RPM, people would lug them around and rattle that 5th gear nut off. I have had several friends with NV4500 trucks and nobody had that problem. But we were all young hot rodders that never lugged anything just high RPM use from us lol. I did have a friend break an input shaft on an NV4500 but that is really the only carnage any of us had.