I just got ripped off, badly, by a mechanic in Vegas, and am having a leaky transmission (damn borg-warner crap). I paid to have my transmission repaired when it failed, it was the original transmission and I think it lasted 124k miles.
There are incompetant fools in the transmission business. There's a good trans shop in Tucson (I used to live there), I'll see if I can't recall the name... George's Transmission? N. of town somewhere. Older guy, not in a big hurry but does good work.
Everyone slags those little aluminum BW transmissions, but they are fine, and very reliable when maintained. If your motor is good, and you're happy with an automatic, it's probably easier and cheaper end-to-end to keep the little BW.
You cannot switch to a "modern" auto trans without changing engines to match it.
There's an auto parts store I used to patronize, down on 22nd st, can't recall the name. They have a machine shop. In a mini industrial park out back is a guy named Ray Buckner. He built the 304 v8 in my Gremlin. He's a little bit of a nut, has a messy shop, usually a bad sign, but he has a "clean room" for building motors and he did a good job on mine. He's... let's say, bad with schedules. Does good work though and didn't do that "Ford or Chevy" thing with me.
There's a parts yard, Millie's, in town, she has some few AMC stuff, but there's not a lot I ever found in Tucson. Some big