major vibration problem after driving 65mph for 10 - 20 minutes on 1996 Lexus LX450

my car begins a major vibration, accompanied by power loss, after 15 min driving at 65 mph. Pull off freeway and drive on surface streets, problem disappears. Tires/balancing ok, shocks replaced, tuneup done, brakes and rotors checked.

What else?

Asked by for the 1996 Lexus LX450
You have got to determine if its powertrain related or wheel/tire related. A break down in the ignition could cause a vibration but should set a Check Engine Light. A professional scan tool can be useful in diagnosing engine or transmission problems. It hard to guess without being able to experience this problem first hand. Can you tell what area of the car vibrates , front/rear left/ right? Try rotating the tires and see if the vibration changes. Can you feel it in the steering wheel or is it more the whole truck vibrates?
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I had the same thing happen to me. I took it to a toyota dealership they wanted chage me 1200 rip it apart. I ended up googling my issue and it turned out to be my front throttle it was hanging from a thread. Look at that.
This was my question, and many thanks for the feedback. After a lot of trial and error and fixing lots of stuff that needed fixing but did not solve my problem...we got it.

It was a rod connected in some way to the master brake cylinder and it would work loose and begin to cause a light braking, which caused the huge vibration. As soon as it was properly adjusted and tightened down, it was all fixed.