I a looking at rebuilding a 700r4 tranny for my 82' Diesel Blazer which has problems holding 4th gear. I do a lot of towing (trailer approx 2500 lb loaded) so it needs to be up to the loads. Am going to start with an 88' onwards unit as a core, what are the worthwhile upgrades to do ?. Do you need any special tools, I have started to read up on it with the ATSG and Haynes manuals. Am hoping that someone with hands-on experience can help me out with some advice. I have worked on ZF autos from Range Rovers so not a total novice.