Vibration

When I put my 87 Horizon in drive it causes it to vibrate. If I park facing down a small hill in the driveway it will vibrate in park until I let off the brake and let it rests on the transmission in park. It seems to me that when ever I put torque on the engine it moves too far on the motor mounts and causes it to vibrate. My first thought was to repalce the motor mounts. After repalcing all three it didn't help and it seems to me that it is getting worse. Any ideas? Thank you in advance.

Greg
blumax32

a little late now, but has the engine been rebuilt at all? if so the balance shafts could be out of timing with the rest of the engine. was there anything that seemed to happen prior to this vibration?