2000 caddy seville sls with the shakes

I tried rebalancing the tires and replaced the rotors. I have been told I may have a bad tourqe comvertor. What do you think?

How about a more detailed description of the problem.

When do you feel it. When is it worse, (speed, part of trip time of day etc.) Any other problems with the car? Any history of like or maybe related problems?

It only shakes at 65 to 75 MPH. Otherwise the car runs very smooth. It brakes well and accelerate well.