Automatic Transmission problems of the 1999 Chevrolet Lumina

The contacts owns a 1999 Chevrolet Lumina. The contact stated that when the vehicle began to shift from third to fourth gear the gears would stick and the vehicle would lunge into the next gear. The dealer inspected the vehicle but was unable to diagnose the failure. The manufacturer was not contacted. The failure mileage was 162,000 and the current mileage was 163,700. The VIN was unavailable.

Vehicle experiencing roll back; whenever vehicle is on a incline it would roll back if brake or acelerator pedal was not applyed. Dealer notifed and inspected the vehicle and informed that the vehicle was design that way. Can NHTSA provide addtional informtion on this matter.