Has anyone ever noticed this with there stock driveshaft? The T/A starts getting some vibration at about 70 MPH and gets stronger the faster you go. The front end is all new and so are the tires, Ive had the tires re-balanced thinking that was what the problem but it was'nt. I can get the stocker balanced at Springfield driveline for $25 but I would'nt think the thing would be spinning fast enough to cause vibration with 2.73's.

 

ttt

 

If it's out of balance, it could certainly cause a vibration. Some other things:
bent axle, u-joint, rear-end bearings/axle bearings, torque converter, bent wheel, slipped belt in a tire(can still balance ok). An experienced mechanic should be able to narrow it down by just taking it for a drive.