1970 Chevy Nova Driveline Vibration

Shakes or Wobbles problem
1970 Chevy Nova V8 Two Wheel Drive Automatic N/A miles

I have a 1970 Nova. The problem that I'm having is at high speeds around 65-75 mph. There is a vibration throughout the car and can't really pinpoint the problem. The vibration causes the seat to shake and I can feel it under my feet. When I am accelerating and let off the gas, the vibration is more intense. I replaced the U joints and had the tires balanced over and over. I just recently had new upper and lower bushings & ball joints installed on the control arms on both sides. Do you think the driveshaft could be unbalanced? Please let me know.

Thanks.