After rebuilding the 8L90e and diagnosing that transmission to death, I finally decided to just give up on that transmission and source another low-miles transmission. I was able to find another 8L from a wrecked Yukon. Since the Jeep is still in Alabama at RPM Extreme, I decided to crate the new(er) trans and send it UPS freight. The transmission was installed, and the subsequent test drive was positive with all gears engaging properly. There are still outstanding issues with which TCM to finally use with this trans. I have 2 T87A TCMs from 2018 plus GM vehicles that will be considered, however these TCMs are locked and difficult to program and tune. Jon at RPM Extreme has an earlier T87 TCM which is currently working in the Jeep, but it does not have the correct calibrations for the installed transmission. GM has really created a mess with this transmission design, and I can certainly see why dealers simply warranty R&R these transmissions when they come in with service problems. One thing to investigate with the old transmission will be the stator shaft condition as it seems the shaft is not allowing fluid pressure to remain in the torque converter clutches during shifts. One thought is the stator shaft was slightly bent, or the bell housing has been tweaked and not aligning properly because of the donor vehicle accident. The stator shaft alignment is integral to TCC pressures and shift timing, and very expensive to replace, both parts and labor.
I am hoping to have the Jeep back in Texas and on the local roads by the end of April!