Hey Roadking..... I'm a new member and just read your post after I joined. My 2002 Sienna started shaking too. It is smooth steering at about 65 mph but when I push it to 70 the front end begins to shimmy and shake. Rotor's, brakes, and steering components have been ruled out by my mechanic. He suggested tires and it does look like I need them.
Have you resolved the shaking problem you had?