8L90-E problems, Help!

Recently installed FBO ported Lt2 im, zr1 tb, rotofab, and longtubes on my 2016 Camaro SS
Car was being tuned and something happened that the tuner has never seen. While in manual mode during a WOT pull the transmission tried to downshift to a lower gear so in fear of hurting the car the tuning had to come to a hold.
Shortly after the install was done I myself noticed the same thing while moving the car in manual mode, upshifted to third gear then all of a sudden I see its trying to downshift to 1st. Never occurred prior to bolt ons.
Any help would be greatly appreciated, my assumptions is the tcm is taking a crap.:banghead:

You could be right about the TCM, BUT it needs a diagnostic. A GOOD scan tool is a must. Need to monitor things like input and output speed sensors and if there are any codes in the ECM or TCM that can affect the trans. Also would be prudent to get your stock tune and do a compare to see if something was accidentally changed that could be causing the issue.

Better save a log of all the PIDs capturing the unexpected downshift and review it, an input somewhere is causing this. I would be floored if it was a bad computer causing this, really makes no sense.

The 8l's are known for having valve body problems, but that's almost always a 1-2 upshift issue. I've never seen one just downshift unless something was off in the tune or especially with the torque model calculations.