If you have aftermarket rims, than it may be the Torque setting of the lugs. After I painted my calipers over July 4th weekend, I went for a drive. I was puzzled to find out that after I hit 60, the entire car became like a giant paintmixer... Went to my buddy at Discount Tire, where they retightened the lugs to the proper setting, and guess what? No more shaking... Good luck to you man!
