Caught Onstar being used to remotely put truck into limp mode and can only run in 1st gear. So do I need to take out that onstar module or what? This is a cyber attack recorded over a spectrum analyzer.

Well that sucks! I’d ask a sub that has automotive techs in it. If it can force only 1st gear, removing it might be a kill switch.

The fault is probably being reported out through onstar. 

Dude you tripped your silent alarm. Call OnStar. 

Here’s the directions if you want to do it yourself 

Insert your physical key into the ignition and turn it to the ON/RUN position (do not start the engine).
Watch the anti-theft light (often a padlock icon or “Service Theft Deterrent System” message).
Wait 10–15 minutes until the security light stops flashing or turns off.
Turn the key to OFF for 30 seconds.
Repeat this process up to 3 times, then attempt to start the car 

Here’s a video how to reset The anti-theft relay. 

https://youtu.be/4ee1dJ1yuzY?si=jDsV11f34uHJQPgC