Engine Head Gasket Failure problems of the 2013 Chevrolet Tahoe

While driving vehicle continues to drop into reduced power mode causing a jarring motion as it drops a significant amount of speed,almost causing multiple accidents. The check engine light comes on, traction control turns off, stabillitrack turns off, and engine goes into limp mode and starts shaking and jarring. The same 2 codes continue to come up in diagnosis. P2135 and p2176. I have taken the vehicle to three mechanics 1 of them being chevy its self. With no solution found. I have had the acceleration pedal replaced, the wiring replaced, the ignition switch and relay replaced had the throttle body connector replaced, the throttle body and gasket replaced 3 times. I have done everything recommended by all shops including chevy. Please help as the truck has been in the shop more then it has been on the road and I have almost been in multiple accidents as the truck is difficult to control when the issue happens.