I have the exact same problem as you!!! Only my car ran super great and smooth and developed the vibration you are talking about. I have owned this car for 6 years, 1972 Dodge Charger with rebuilt 1990 360 motor. 9:1 stock or small upgrade cam. Davis HEI Ignition, Holley street avenger carb. B&M Flexplate, Mopar performance 145K torque converter with neutral balance (no weight(s)). When torque converter was installed 5 years ago the shop had to knock off the weight to make converter neutral balance as B&M Flexplate s already balanced. Car ran smooth and strong for many years. 1 year ago I noticed a little vibration upon acceleration. Got progressively worse over the last year. Sure enough, tranny mount was bad but that stopped clunking , not vibration. Rebuilt carb, new plugs, verified timing, verified spark plug wire order. Car runs really strong but vibration still there. 18" vacuum at idle and needle rock solid so I cannot believe it is a tuning issue. I replaced harmonic damper with Summit Racing damper #163318 for external balance 360. My old damper looks exactly like Mopar Performance P5007301. If anything vibration may be worse. Then replaced motor mounts. A little smoother but vibration still bad. So bad now I only drive car to take it to get opinions from expert mechanics. For sure it is engine/balancing/torquue converter. Exact same smyptoms as Kielbasa's orginal post only mine have developed over time. Dash, steering wheel, and floor pan shake at anything above idle. Help!!! Thinking of rebuilding original damper but now I am getting into replace my new replacement parts...