It's obviously something to do with the drive shaft you put in it. Put new universal joints and carrier bearing on the drive shaft you took out and put it back in.

 

So if you used different parts to make up the driveshaft you might need to balance it at a drive line shop. Also if you replaced any u-joints did you phase them correctly?

Might also want to check the rear pinion nut to ensure its tight.

jrc

 

Update
I got busy at college and didnt have time to work on it. It ended up being the pinion bearings. I was going to replace them but instead decided to swap axles out of the parts truck. Disadvantages of that is that they are 4.10 not 3.55 like I had. Advantage is that they are limited slip and the old ones were open.