It's because GM was constantly upgrading weak links in them. some are interchangeable, some aren't.Best bet is to bite the bullet and let someone who knows what they're doing rebuild it.I paid 600 to have mine done on my '99,including Corvette servo.That was doing the r&r myself. Toss in fluid, new converter,beer and bandaids (and 40 bux for the new NSS that I destroyed before I learned that GM hotglued the connector on)and a few bux on a can of flush for the tranny cooler, and you're around a grand, give or take. OR, if it's not dependent on being used as soon as you finish, buy the ATSG manual, and the dvd on rebuilding them, and do it yourself.Once a transmission is dead, honestly,trying to go cheapo is just buying yourself a headache.Be forewarned, there are several sealing rings that have to be put on with special tools, but if you're crafty, it can be done without the insanely expensive tools that pro's use.You still need the rear clutch spring compressor, and bushing drivers to do it right though.I did my Suburban's 700R4 successfully, but it was a challenge without all the right tools. My G-body's 2004R is next, unless I stumble on some money, then I'll just pay someone, lol