Originally Posted by gone postal
Very likely they forgot step one of changing a U-joint: Mark where the driveshaft was.
If the driveshaft isn't put back in the way it came out, you could have balance issues.
X2. The first step in removing any type of drive shaft is to mark it's top and/or bottom. After re-installment, the driveshaft must go in at the same position.
It's also possible the shop that replaced the u-joints pinched a needle bearing (or had one or more drop out) when installing the new u-joints to the drive shaft. Or you just got a bad u-joint.
In any event, take it back to the shop that did the work and have them correct their apparent problem.