if it was a u-joint it would get better going straight.is it possible the tires were switched left to right?most of them are directional.it sounds like a balancing problem.even big blobs of grease on the insides of the rims could cause that,or mud.borrowing someone elses wheels is where I would start.as far as the brakes if the allen stop screw is set too tight that can cause the outer pad to hang up and overheat the brakes