Has anyone here successfully gotten a 6 speed pcm (built-in tcm) to work on an 8 speed (separate tcm)

I copied all of the settings over with HPTuners and used AlphOBD to set the VIN. It's "mostly" working but I see a constant U0402 Implausible data received from TCM and the shifter knob is acting weird, sometimes not allowing me to shift from P to D/R.