You've got yourself an NV4500, the 8.1L and Dmax came with the ZSF-650 6 speed. 4500's are stout, my '95 Sierra 3/4 ton came with one. The 3rd and 5th gear synchro's go out in high mileage situations, that is your only thing to worry about. My stock clutch went out at 135,000 miles and I went with a CenterForce from Advance Auto. Clutch pressure went from soft....to brake pedal hard - but it was a very good clutch kit, wouldn't do anything differently.
Hope you like your NV, I'm going to swap one in my next GMT for sure - no sissy 4L60/80 for me