Engine cutting out sporadically

LS1 engine in a 2003 Chevy SSR for no apparent reason goes into limp mode then stops. After waiting a minute, it starts and runs fine sometimes for the rest of the trip, sometimes for just a minute. Sometimes I can run an errand or few and not have a problem. Codes are P0120, P0220, P2135. In the past year, the throttle body (GM/Delco), X-Link, and gas pedal have been replaced.

Engine has been rebuilt with performance parts, and had performance tunes a few times. Magnacharger 2.3 L supercharger.

I'm really hoping that somebody will come back and say, That's an easy one - just do this...".