The 4T65eHD will need to come out by dropping the cradle and detaching it from the engine. The transmission is not that difficult to rebuild and a complete rebuild kit runs about $100, add in a few more parts like shift solenoids, you are probably around $200. A transmission rebuild is just a parts replacement job but there are lots of parts that need to be put back exactly. If you purchase the rebuild video or rebuild manual it will guide you though the step by step process.
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "