I believe it was more stout and I could be wrong, but I don't think they resolved the non-hardened shaft and the pressure control solenoid issues until maybe around 2003?
Exactly. IIRC the HD had a beefier differential, but that was it.
Don't be having that transmission constantly shifting between 3rd and 4th, and that input shaft should last a good long while. It's possible to replace that shaft itself, but does need the car lifted off the front subframe if doing it as a driveway project!