Automatic Transmission problems of the 1996 Acura TL

The problem at certain combinations of rpm and speed, the engine labors. It causes excessive vibrations, which continue until either the speed or rpm is changed. It is not related to traveling up or down an incline. Taken to Acura dealership several times and they stated they were unable to reproduce the problem but noted that it shifted hard on 1-2 upshift and flushed the transmission system. This did not fix the vibration. When I took the car back in for same problem they stated the front brake rotors were warped and replaced front brake rotors and pads. Took car back to dealership with same problem again and the tires were then balanced. Problem continued so I determined they couldn't find the problem and gave up.