Brakes work fine if pedal pressed slowly, dont work if pressed suddenly
 

I just replaced my front stock brakes on my 1973 with a Wilwood kit with 6 piston calipers. The brakes were bled and the pedal is hard and feels normal. If I press the brakes slowly, they work fine. However, if I suddenly press the brake, the brakes dont work at all even though the pedal stays hard. I cant figure out why. Is there some sort of bypass in the master cylinder when too much pressure is applied? More detail;

Before; stock front discs + drum rears with Classic Performance Products aluminum master cylinder with the built in proportioning valve -- worked great

After; added a Wilwood Dynapro front big brake kit with 6 piston calipers and 12.2" rotors. I also replaced the brake booster with a new unit.

Again, I am trying to figure out why the new set up works fine when I press the brake pedal slowly, but absolutely do not work at all when I jump on the brakes and press the pedal suddenly and strongly.

thanks,
mike