Many cars with 2-piece drive shafts and center support bearings have drive shaft vibration issues. Other than the above mentioned things to look at also look at things like the bushings that hold the diff. including the one right at the front. also look at the sub-frame bushings. Every thing from the front of the car to the back needs to be attached nice and firmly and in a straight line. I've seen people have a-little luck fixing minor drive shaft vibrations by shimming the trans mount up or down or the front of the diff. up or down but never tried that myself.