2006 Nissan Altima vibration in steering wheel

I just had 4 new tires put on my car, but, still feel a vibration in the steering wheel and when I brake at high speeds, the steering wheel shakes slightly. The mechanic said my brakes were fine, the wheels were balanced for a second time and seemed to be better, but, I still feel the vibration, any ideas or suggestions what to do next?


Thanks