It might be a transmission problem.Two months ago, I went to LA and rented a car.
When I drove on to high way, the car only ran 20 km/hour even though the rotation meter said 5000 rpm. I drove back to Hertz and asked them why you gave me such kind of car. They told me that this was transmission problem. So, I think that your car is similar to this situation. You can go to COSTCO or Canadia Tire to change tramssion fluid.