Vibration under load

[SkinsandJrfan]

I am having a heck of a time getting an answer on this situation. 68 Camaro running a 383 with a Borg Warner 5 Speed with 10 bolt rear end. Tore the car down, changed the rear suspension and front subframe. The only thing I changed between the Engine and the rear was the univeral joints in the drive shaft. After getting the car on the road, I have a vibration in 2nd, 3rd and 4th gear but not 5th nor when I put the car in nuetral and coast. It vibrates when I am accelerating or down shifting. I have no clunking sound when engaging the gears. There is no place in the rear U joint with minimal in the front.



Any idea what this vibration might be caused from?

Thanks
Brian