When the brake rotors start to warp there is a noticable "chatter" which occurs when braking at a highway speeds. When braking at slower rate of speeds it is not noticable until the brake rotors become more warped.
It appears that your car has several problems which may affect your steering and braking systems. If it was my car I would not drive it (expecially at highway speeds) untill the problems are fixed.
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles