P0758 Electrical Diagnosis

[Danster813]

I'm helping out my neighbor and am in need of some resources to help diagnose what is causing the electrical fault on shift solenoid B. Current symptoms are that it initially shifts hard into reverse/drive, shifts violently when downshifting into 1st gear, won't shift into 4th gear, and the A/T light is illuminated. I got the TCM refurbished by All Computer Resources and remounted it back on top of the transmission. Before doing this, I believe I tested the appropriate wires to see if they ohmed out but I could have misread the patchwork of wiring diagrams I found online. The problem persisted after the install and the car was able to shift into 4th for a limited time after clearing the code several times. Later on, I ended up swapping the solenoid (believe it should be the one with a blue connector) with one I got from the junkyard. Not sure what the resistance should have read but everyone I found on the yard read 2.4ohms. I powered them with a battery and they all clicked. I ended up replacing the solenoid, changed the filter, and replaced the old fluid. The fluid was black as night and there was a fair bit of crud stuck onto the magnet. After all that the symptoms still persisted. A few days later I find out that there is actually a TCM relearn procedure that can be done when the ignition is in the on position. My neighbor tried it and the issue went away for a few minutes but then returned. Another day he texted me that he started the vehicle and the issue was gone for 15 minutes. That actually has me a bit worried as it seems like the unit is behaving marginally better as a result of the fluid drain and fill. The unit has likely never had its fluid changed and I'm not sure how that neglect can be contributing towards the current electrical issues. So I'd say I'm split 75/25 on the culprit being a refurbishing dud for the TCM or the transmission being toast respectively. From what I've read, this issue is purely electrical 99% of the time, so idk wth is going on here. Are me and my neighbor the 1%? If any Mazda Techs that are familiar with these FS5 units can spare some wisdom it would be greatly appreciated.