could be idler arm,centerlink or tie rods. If you are sure you can rule out wheels and tires then look at aforementioned components. If they dont have sufficient play to warrant shimmy could be drive train. Just my 02cents upper and lower control arm bushings with Paul Gray poly bushings, new shocks, new lowering springs and fresh alignment. I've had the wheels in numerous times for rebalancing and even changed tires. Could it be defective wheels (MASITALY PRESIDENTS) or have I missed something here. Thanks for your help.