My SXT has a problem at all speeds above 30mph or so. When you keep the pedal down just enough to stay at that speed it seems to be going from OD to 3rd back and fourth. The service dept. did a tran. service $150 then they say tourqe converter $780 still same problem. If you put your footin it it goes no problems. The car has about 74,000 on it. Now they have had my car for five days they tell me the tourqe converter needs to be broken in. IS THIS BS ?