Vsa Warning Light On problems of the 2006 Chevrolet Avalanche

I backed out of my driveway stopped my truck like always put it in d to drive heard a loud clunk noise and now I have 1 and 2 gear only to use the truck was stationary was on a main road I changed the transmission fluid screens filters everything flushed it out and still the same thing a lot of people are saying it's the sprag unit I have no idea what that is I have only hauled a few things with it when we were moving we only moved eight miles down the road used a trailer and the tow gear that is on the truck. Also about a month before this happened the stability system light came on and said disabled but has not done it since also my truck is very clean always serviced according to the manual and is in very very good condition.

The contact owns a 2006 Chevrolet Avalanche 1500. While driving 60 mph, the vehicle decelerated. The vehicle was taken to the dealer, but they could not duplicate the failure. The most recent failure occurred on February 25, 2008 while stopped at an intersection. The contact stated that the failure was intermittent; however, the stability light illuminated during the last failure. The vehicle will be taken back to the dealer for a diagnosis. The manufacturer was notified and the failure was escalated. The contact will receive a call back. The current mileage was 20,000 and failure mileage was 18,000.