I'm not trying to be a smart ars here. I know this sounds pretty basic but you never know.

Are the drive lines front and rear line up properly ? I'm sorry I don't know the proper terminology but both ends of the drive lines have yokes for the u-joints. These need to be aligned.

I had a friend that had a similar problem and his rear drive line was off. On his we had to pull the rear off and pull it apart and align them and it solved the problem.