2000 Range Rover 60mph and higher vibratiion

Bought a 2000 Range Rover used, drove it about 350 miles home and it drove great with no problems. When I got it home it needed new tires and front brakes. After it got new tires and front pads and rotors it developed a vibration at 60mph and dissapates some at 70 but is still there. The tires were found to be bad so Dunlop replaced all four, didn't help with the vibes. Replaced front rotors with to new ones, didnt help. Both drag link and track rod and both tie rod ends at the ends of both were replaced, didnt help. It seems to get better if the SUV sits for a few days, but after its driven for a few days in a row it is more noticible. Also while driving at highway speed or in the "wobble zone" after I hit a bump the steering wheel will jerk to the either side, usually the right. Not to the point of losing control, but im sure other drivers are thinking ive been drinking as its isnt staying straigh. The allignment has been done and when there are no bumps it drives straight. The front and rear drive lines have been removed and driven without (seperate times) with no change and if you get it up to vibe speed and throw it into nuetral there is no change either. Its been to three different mechanics now and they are all throwing thier arms up. Anyone have any ideas? Is it possible this is an engine mount issue? There really are no other signs or symptoms of any kind. Other than the rediculously annoying viberation at the exact speed I like to drive at, its a great SUV. PLEASE HELP!