I am trying to get some information on suspension fixes. My 2000 Avalon (109,000 miles) is shaking at freeway speeds. I have had the front and rear end aligned, rotated tires and had them balanced and filled with Nitrogen. Car drives fine until I reach 60 to 65 miles an hour then the steering wheel shakes rather violently. Shaking lessens as speed increases and there are several "sweet spots" about 73 mph and 78 mph where vibration is acceptable. Does anyone have any idea what is causing this and how to correct it. Thanks for your help.