2009 GMC ENVOY Electronic Stability Control Esc Problems

WHILE DRIVING AROUND TOWN, I HEAR A NOISE, THAT SOUNDED LIKE A FLAT. THE TRUCK BEGAN TO SLOW DOWN ON ITS OWN, WITHOUT ME APPLYING THE BREAKES. I MANAGED TO GET THE TRUCK OVER TO THE SIDE OF THE ROAD. THE SERVICE STABLTRK LIGHT WA ON, THE BRAKES LOCKED UP. I HAD IT TOWED TO THE DEALER WHO DID 1400 DOLLARS OF WORK ON IT , BUT STATED THE COULD NOT GET IT TO DUPLICATE MY COMPLAINT. 7 DAYS LATER IT REPEATED THE SAME THING, I HAD IT TOWED TO THE DEALER. THIS TIME THEY TOLD ME THAT I HAD CONTAMINATED BRAKE FLUID. I WAS UPSET, AND FELT I WAS BING JERKED AROUND. I HAD IT TOWED HOME. HAD ANOTHER MACHANIC TEST THE BRAKE FLUID, NEEDLESS TO SAY, IT SHOWED TO HAVE THE NORMAL AMOUNT OF CONTAMINATION FROM ROUTINE DRIVING. HE ALSO COULD NOT GET IT TO REPEAT THE PROBLEM,...