There will be a vibrating feeling in your wallet...jstang209 said:
Check the alignment of the yellow paint mark on the driveshaft with the paint mark on the rear axle flange.
Having a machine shop balance your stock drive shaft is $35-$55 depending on the labor rate in your area.
Cheapo test method: Put two worm gear radiator clamps on the driveshaft next to each other. Start with the screw 180 degrees apart. Drive it, if it vibrates, move one clamp so that it is 200 degrees apart, drive again and note the change, if any. Move the one clamp some more and repeat the process. If you get the clamps to the point where both the screws are side by side, and it still vibrates the same, the driveshaft balance probably isn't the problem.