Auto transmission sluggish

92 cavalier automatic transmission is sluggish on take off, does not matter whether engine is warm or cold. Just doesn't shift until the RPM's are very high.
Also, while in Drive, and holding the brake at stopped, the dashboard shakes, and stops shaking only if car is in Neutral. (Shakes also in Park).
The fluid level is correct. The mileage is 260,000 Km. Car runs fine. But I am thinking that the auto trans is pulling the engine rpm's down when the car is stopped causing the excess vibration on the dash.
Any idea why?