Transmission Gear Slipping problems of the 2009 Mercury Mariner

The contact owns a 2009 Mercury Mariner. While driving approximately 65 to 70 mph on normal road conditions; the transmission slipped with excessive vibration. The engine began to rev and the rpm's were high. Suddenly, pressure was applied to the accelerator pedal, however, the response was minimal. The contact was able to drive onto the emergency lane and resume normal operation. An authorized dealer confirmed that the failure was contributed to the transmission over drive piston. The vehicle was repaired. The failures occurred whenever 5th and 6th gear were engaged. The identical failures occurred on two separate occasions after the service repairs were performed on the vehicle. In addition, the vehicle rolled while stationary on an incline. The contact had concerns of the safety risk involved. The failure and current mileages were 13,088.