While driving 65mph and above a vibration starts in the rear, increases, fades

Not sure what you mean by disc. There are disc brakes on the front and the pads and calipers seem to be working fine. The rotors aren't warped. I recently replaced the tie rods as they were wore out at the bushings. I had it lined up as well. Thank you for your reply.

Thank you for your suggestions. I replaced the u-joints and the center support bearing (carrier bearing). This didn't seem to help much. I did notice that my shocks were worn out in the process of the above. In replacing them with Monroe gas shocks I saw a great improvement in the ride. The vibration is still there but a lot less noticeable.