You might try checking (or have the shop check) the alignment of the driveshaft. The two pieces need to be lined up straight within a pretty tight tolerance. There is a special tool (of course) that you can use, but I used a 48" level and some wood blocks to get the job done. There are also balance marks on the shaft that should be lined up with factory marks on the differential flange. Overall it's a fairly involved process to get a new driveshaft setup correctly. The factory service manual really helps too.