gonna have to grab each part and try to move them your talkin about alot of stress at those speeds so I would proly look more at subframe mounts. you may even have to grab a pry bar and lightly pry on parts to see if they are moving. This is all if the accual play is in your rear end jack up the front of the car and grab the tire and see if you have any play in the bearings or tie rod ends. Any unsal tire ware on any of the tires inside or out?