Do I need a new transmission, or am I missing something?

We have an '08 that we purchased in 2022, now with just under 249k. Everything has been running fairly well, until recently, when the vehicle randomly shut off, and after restarting, came on with a CEL, red triangle, and (I believe) the VSC light. At this point it was in limp mode and luckily was only 2 minutes away from the house, so it was driven back home.
After I hooked up a regular OBD2 reader, I got a P0A7A and P0A92, so I shut the car off to look the codes up, and later came back with Techstream to pull the subcodes. I had the vehicle in accessory mode, but before I could get Techstream connected, the instrument cluster and so such seemed to fade out, so I tried to start the vehicle, but it seemed that the 12v was too far drained. I hooked up a jumper pack, then fully started the car, which had lost the codes.
Test driving the car (not any higher than 35mph), the only odd behavior I noticed was that when decelerating without applying brake (coasting down), around the 18-14mph range, the car would start pulsing, which seemed to gradually get worse. This was without touching the brake pedal, so I don't believe it was the friction brakes. Eventually I got the car to throw the codes again by giving it somewhere around 60-80% throttle, which put it back into limp mode.
With Techstream, I pulled a P0A7A-325, a P0A92-606, and a couple of codes that were presumably caused by either of those; C1310 and C1259. The service manual I have indicated to diagnose P0A92 prior to P0A7A, so I went through that procedure, pulled the battery current sensor, which according to what's in my service manual, tested bad. I replaced it with a new one, which tested basically the same as the old one. I believe the testing steps in the service manual are mismatched with the pins on the sensor, so the old sensor was probably fine. Took the car on another test drive and it threw a P0A92-606 right away, but didn't throw the P0A7A this time. C1310 and C1259 were still present.
The service manual at this point indicates to replace the generator assembly (which would essentially mean replacing the transmission). This would seem like the most likely course of action, but I want to make sure that I am not missing anything. We tried to move the car a couple days ago into the garage to work on it, but it shut off a few times, then wouldn't start. I'm fairly sure that the HV battery was drained too far, as it tried to crank but sounded like a traditional vehicle with a weak 12v battery, unable to turn the engine over.

Due to this, and the fact that I am fairly sure that the hybrid battery has not been replaced, I am wondering if it's possible that the hybrid battery could somehow be causing the other issues? I'm not sure if the HV battery was being charged while the vehicle was in limp mode though, so that could be the source of that issue. We have also had some issues with the 12v in the past, despite it being fairly new, but it seems to be unlikely for that to effect the HV system, especially considering the freeze frame data for the codes indicated B+ of 13.65v. I'm going to pull the HV battery since I'll need to charge it anyway, and will check for any significantly out of balance cells.

I was reading about testing MG1 and MG2 with a megohmmeter, and was wondering if this (or anything else) might be worth a try prior to replacing the transmission. Anyone have any thoughts?

To give a bit of additional background on the car, as I mentioned it has just under 249k miles on it, and cosmetically isn't in the best shape, but has been running fine until now. We purchased it in 2022 with a bad brake actuator, and I replaced the brake actuator with one from a wrecked car that had just had a brand new brake actuator installed a few months prior to the accident, so that failure point is covered quite well. Haven't had any other issues with it.

Thanks to anyone reading my very lengthy post.