SAndresen,
I had a 95 with the nv4500.
I ran the bearings out of it in less than 80KM. In my case the truck was only modified by a governor speed limit change (not torque).
My owner manual said it had a life time synthetic oil but as others have found out, regular oil changes, perhaps every 50K or so might have prevented this problem. I had it rebuilt by standard transmission in Texas and had them put in a fully splined main shaft at the same time to help prevent 5th gear problems.
In spite of all this, it always shifted much nicer than my present Nv5600.
Rog