6L80E Stuck in 2nd gear until I clear CEL Codes. Stays in 2nd again when I stop

[TXjeepTJ]

Hi All,

I installed a built 6L80E into a 2008 Pontiac G8. The car wasn't running for 5 years, so idk if that could be causing this, but just want to put it out there.

Whenever I drive and log a scan, it shows the transmission is stuck in 2nd gear (I put it into Drive, automatically goes to 2nd and stays there). I did notice that when I clear the CEL codes, it begins to shift, until I come to a stop, it drops down to 2nd and stays there.

These are the only codes that HPTuners scanner shows:
U0100 (Pending, Current, Permanent) - Lost Commnication with ECM/PCM A
C0460 (SES, Pending)
C0045 - Brake Pressure Sensor B (even though the internet says this is left rear wheel speed sensor)
C0050 (SES, Pending)

[Tre-Cool]

highly likely you have the wrong os in the tcm.

does the car have the original tech still?