Mitsubishi Repair Problems? Ask a Mechanic for Answers ASAP
I can certainly appreciate your tenacity in the matter.... and I wouldn't have sold the car for that either. Scrap is really low right now ($0.02/lb here) but even at that it is a hard sell, let alone at $130.The problem that makes this more or less impossible to diagnose is that you keep switching from one transmission to another and having different problems... meaning each transmission has a problem. If the issue was only that you had X happen like a shift flare, then sure we could speculate on a possible vehicle side problem (rare as it would be), but you are having different issues as the units are swapped.... going from one bad transmission to another.
Given the amount of time you have spent and who knows what on transmissions, not to mention not knowing the history of any of these transmissions at this point, the best thing to do would be to buy a new or remanufactured unit or if you really think you have a solid builder among the various transmissions you have bought, take it to a shop for overhaul and proper building with new components instead of trying to mix and match. Anything else is going to exercise your wallet and your patience to say the least.