I mentioned months ago in this thread that it was probably my tires, I pulled it out of storage this week, and I'm getting new tires this weekend or early next week. I took off my wheels and inspected everything carefully, the wear on the tires is so mis even and the metal wire is showing on one of the rear ones! I'm assuming new tires with balancing will fix it.

 

Also try the idler arm, mine is having the same problem except aroung 75mph

 

I agree, idler arm. You probably need to replace the bushings. I got mine from victors imports for $15. Made all the difference.