I had the same problem ... 4 times while driving. Dealer fixed it 4 times. Right? They finally replaced a "black box and a wiring harness assembly". That finally fixed it.Driving down the interstate, my 2011 Enclave gave me the message serve stabilitrack and engine reducing power. My check engine light did not come on, but my power was reduced considerably. Using my OBD2 scanner that was Bluetoothed to my phone I saw that there was a pending fault. It was throttle position sensor circuit out of range. As I found out later when that particular code is thrown the car goes into limp mode and disables the stabilitrack. I replace the throttle body with the throttle position sensor as one unit and that corrected my issue. I was at a loss because there was no check engine light, luckily I had a pending code on the OBD2 that pointed me in the right direction.