These transmissions are getting harder to find in good running shape
as they were discontinued somewhere around 1998. You can find them on Car-Part.com in used unknown condition for about $300 but its a crap shoot. Buying off someone that you know is a better idea.
It looks like the one on my 4.9L project may need a rebuild but we've decided to do the rebuild here. You can restore these boxes to better than new performance for about $500-$600 in parts. The rebuild process is lengthy but nothing more than carefully replacing the internal parts like clutch plates, bands and maybe a sprocket in the correct order. A remanufactured 4T60e will cost you about $1600 so they can be costly.
" 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 "