Steering All Over the Place at 55mph+

What tires are you running? If all the suspension parts are good and tight. You most likely have an alignment problem. From the sounds of it, the car wonders when hitting bumps and slight steering input. If the car is has radial tires (most likely) the car has bias ply alignment specs if it was taken to a run of the mill shop that does alignment based off of book spec. @72bluNblu talks a lot about suspension setup. Look up his posts.