I was on the freeway in pretty heavy traffic. the traffic started to disperse and as i accelerated, the notification chime came on and the dash message said "stabilitrack off, traction control off, engine power is reduced". i could not drive any faster than about 20mph and it was jerking a bit. i pulled over and pushed the onstar button. they sent a tow truck and after sitting on the road for about an hour, when i started the truck again, the message was gone. i had it towed to the dealer anyway, and was told that it is a sensor problem, which is not covered under the powertrain warranty. i have a friend that has a 2007 tahoe and she had the same problem. also, according to a few message boards, many other people have had this problem also. *kb