I had the same problem (98 SVT), people told me the same things. I even put a dual-mode damper on, helped a little, but I knew the annoying vibration wasn't always there.
Turns out the bolt on the left-support insulator (mount on TOP of the trans) was broken, and the rear roll restrictor was flattened a little. I didn't even know the mount on top of the trans was broken untill i went to take it off when i pulled the trans and it fell apart lol. I replaced both mounts and the vibration was gone =D
Its been my expierience any little vibration that wasn't always there, and the engine runs fine - inspect all the motor mounts.
