03 Camry XLE V6. When driving over 50 MPH the car feels like it is behind a heavy tractor-trailer. It rocks and drifts from right to left then back. It is though the car is on a rail and following a track. Even does it on new pavement so it is not "riding the grooves" in the road. Dealer has rotated and balanced all tires and alligned the front end. Everything was "normal". They claim that the "feel" is normal. Any suggestions?