[Bob]

You said that you installed new motor mounts. Were they stock replacements, or were they Polyurethane? If you use a stiff motor mount, it can transfer vibration to the entire car at certain rpm's. I have "Prothane" mounts in my '68 with a 331 stroker. It will send a vibration through the car at about 2,000 rpm. After some investigation, I figured out that it was the new motor mounts.