While under light acceleration, the vehicle violently down shifts causing the rear wheels to briefly lock up around 45mph. The vehicle traction control activates on dry road way but no check engine light is displayed. The dealership claims the valve body in the transmission is to blame and has a three month back order due to several vehicles with the same failure. The safety issue could be when the rear wheels breifly lock up during wet or slippery conditions and could cause the vehicle to lose control causing a crash.