it's probably both the tires and the brakes. Go get a brake job, tires balanced, and a wheel alignment just to be sure. It's most likely the brake rotors. If the problem was solely the unbalanced tires, it would shake all the time, not just at high speeds. Definetely get an oil change. Old oil is BAD. Don't know about the 4ws light, my lude doesn't have it. I wish it did. See how the car runs after all that.