Some of the earlier 700R4 transmissions were troublesome. I had one in my 86 Suburban that caused a lot of trouble. The engine (350) was fine when I sold it at 183,000 miles but the transmission had been rebuilt once and needed to be done again. I don't think that I was hard on it. No major towing and I had a good aftermarket cooler in line with the towing package cooler. I looked into the issue with the intention to rebuild it better the second time and learned that there are a number of upgrades that are required to keep the transmision alive. If you are going to go to the effort to install one I suggest you get a reputable shop to rebuild it first and make the upgrades so you won't be cursing it later.
