[MARKDTN]

OP-where did you get it from? Perhaps it has been upgraded. My '83 K20 the original transmission went close to 80k miles before it ate the pump. It was my DD then. Pulling trailers, loaded- not particularly gentle with it. The GM dealer put a pump and a torque converter in it about 1994 and it went more, I don't remember how far. It died again about 1997 and it got a GM reman which I should have done in the first place.

But as mentioned above you absolutely want the '87 up upgrades done or you will likely have issues sooner than later.