at that point I'd be checking for trans alignment.... wonder if it's the OE trans, or if the other owner had a unit exchanged. I've seen them break, but that was on some trucks with some pretty aggressive tuners. Billet piece fixed those, but like you said, those were later builds. I have a customer with a 92 4x4 diesel that has a tick over 100K miles on it, and it looks like new. It's a spectacular specimen of a 1st gen.