Vibrations coming from the driveshaft

I have just recently changed all three u joints on my 95 ext cab chevy p/u. After putting the driveshaft back on, i drove it. I feel a vibration coming from what i think now is the drive shaft. What could i do b/c i want this to stop. i have 22's in the rear with a 4/6 drop. im fixing to install bags. Is there something i need to adjust or add to stop this vibration? Someone letme know