Steering Shake

2006 Altima owner...few weeks ago I noticed steering shake when braking from highway speed (>100Km/h) and it disappeared below 80km/h. I suspected warped front rotor so replaced both rotors and pads in the front as a brake job was due. Now I am getting steering shake around 50km/h. I also feel slight pedal vibrations. If I press hard on brakes shaking goes away. Any suggestions? We jacked up the car and inspected the suspension and it is firm. It shakes only during braking so I don't think it is suspension or tires....Any suggestions before my pocket gets any lighter....I also inspected the front rotors with dial ind. and they seem good..