Those platinum plugs could be your problem. These cars seem to run best on NGKs, with Bosch copper (the cheap ones) a close second. Easy and inexpensive to try.

Motor mounts on automatic cars can deteriorate and collapse, to the point where the oil pan is resting on the crossmember. This doesn't make the engine vibrate more, but amplifies the normal vibrations and makes them a lot more apparent inside the car. Usually most noticeable at idle, though there is often also a buzzing at certain RPMs that will come and go while driving.

The intake bellows between the AMM and the manifold can be the cause of a vacuum leak. If a hose or wire rests against it for a long time, it can chafe a hole in it, which can be difficult to detect.