Automatic Transmission Torque Converter problems of the 2001 Mercury Cougar

At 25,600 miles, I brought my vehicle into the dealership to complain about hard & rapid shifting and that my check engine light had come on. They replaced the engine light, but were unable to duplicate the shifting issues. I continued to believe the vehicle did not shift appropriately. At 38,200 miles, with the vehicle just over the warranty period, the vehicle again had harsh rapid shifting while traveling on the interstate during rush hour traffic. Out of fear for my safety, I exited the interstate and was completing a turn when my vehicle stalled in the middle of the road with out any warning lights, leaving me with no power steering and no control over the vehicle. I brought the vehicle to the dealership and was required to pay the $90 diagnostic fee for the same issue that had not been fixed at 25,000 miles while the vehicle was under warranty. They informed me I had a mechanical problem with the torque converter and they would flush and fill the transmissions. They indicated this fixed the problem, but that this was not a problem directly related to the hard shifting and stalling. They could not duplicate these complaints. A little over a week later, the same issue occurred while traveling to work on the interstate. The vehicle was up and down shifting harshly and once again stalled without any warning. I have made an appointment with the dealership to have it checked again. I am worried about my safety and the safety of others with this vehicle. There is no warning when the vehicle is about to stall and both times has stalled while traveling at about 30 - 40 mph.