55nomader

I purchased the Gm connect and Cruise package. The first transmission went with about 4000 miles on it. Performed well out of the box, perhaps little to harsh on the shifts and on one occasion lost overdrive, code said it was electrical,reset and worked fine for about 800miles and then made a lot of noise. Removed transmission,sent to GM and they replaced it and the torque convertor under warranty. (said it was a bushing supporting the main shaft that went bad.
Installed new transmission and now only has forward and reverse.Everything checks out electronically,code is po748 however we cannot get the Supermatic control module to communicate with the laptop for further checks. The conclusion from Gm performance is the Supermatic controller is not working, replace it and the wiring harness which I would do except they will not do it under warranty although it is 3 years and I have 6 months powertrain left.These thing with wiring are over 2000$, would like to know for sure if this is the issue or not. Anyone with same sort of controller issue. It is the second design black box TCU.