I had an interesting revelation about my "bad" transmission. It may be fine after all.
It was getting really hard to get into reverse, then slowly it started not letting me shift down into 2nd on decel. Then finally 1st started giving me trouble.
So I parked it, while I'm waiting for the used MZ0 to arrive, and have been taking my hooptie to work. Yesterday I had to move my Sonic out of my driveway to get a friend's car in to work on. Well, after sitting for 2 weeks, it's gotten reeeeaally bad. Transmissions don't get worse while sitting.
I'm 90% sure that it's the clutch hydraulics. The clutch is dragging noticeably with the pedal depressed. It seems likely that the hydraulic system is not sealed fully and is letting air in. I'm gonna investigate today, and try to re-bleed it.
If it's something simple, I'm going to be so glad I didn't prematurely swap trannies. Plus I'll have a back-up trans when the MZ0 arrives on Monday.