2001 Lexus GS 430 Wheel vibration

Wheel-speed vibration in front end and possibly rear as well felt from 75 to 82 mph. This has been unsolved for 30 months I've owned the car. So far we have tried:
Alignement, twice
New Tires, twice
Front struts and tie rod ends
New rotors
Straightened the wheels at a specialty wheel shop
Road force balance, three times

Sometimes the vibration is very slight, but it comes and goes, sometimes very annoying. Steering wheel wiggles and passenger seat backrest shakes. HELP!