REGULAR OIL CHANGES AT GMC DEALERSHIP SHOWED HIGH OIL CONSUMPTION. CHEVY DEALERSHIP REPLACED TRANSMISSION 2015 UNDER FACTORY WARRANTY. HIGH OIL CONSUMPTION CONTINUED. 2018 ENGINE POWER SHUTS DOWN CAR WHILE IDLING. TOOK IT TO MY LOCAL MECHANIC REPLACED TRANSMISSION. DROVE ALMOST 400 MILES ON "NEW TRANSMISSION" AC NOT WORKING, IDLES WITH HIGH PITCH SOUND WHEN FAN IS RUNNING. NOW SEAT BELTS LIGHTS FLASH AND ALARM DESPITE SEAT BELTS IN BUCKLED POSITION. ENGINE GOES TO POWER DOWN /SAVE MODE WHEN DRIVING ON FREEWAY AT 60MPH ON HIGHWAY. THIS POWER DOWN (REDUCTION) HAPPENS STALLS AND WONT DRIVE. ENGINE CONTINUES TO SHAKE AND RATTLE AFTER BEING PUT IN PARK AND REMOVING KEY (WHEN TURNED OFF)