I have a 2001 Jaguar XJ8 and have had continuing problems trying to eliminate vibrations the seem to be coming from the front end thru the steering column. The vbrations start at 42 mph thru 47 mph. Then at 75 mph a feel a shudder vibration that seems to be originating in the rear of the car and is felt thru the front seat. Thinking this was a classic example of wheel and/or tire problems, I have replaced the tires, load balanced all the wheels, replaced two wheels that were bent and re-alligned all four wheels. Yet the vibrations continue. Could the rotors be out of round? could U joints be the problem? how about loose engine or transmission mounts?

Optional Information:
2001 Jaguar xj8 V8

Already Tried:
new tires, load balancing all four tires, 4 wheel computer alignment, new front end shocks, replaced bent rear draft axle.