Well.. here's the story. I replaced my crap old rotors and pads back in September with centric rotors and Axxis ultimate pads from and rear, turns out.. above 60 or 70 mph when I slam the brakes at those speeds (or even moderately apply good pressure) the pedal hardens up and the car doesn't really stop at all (It's an 01 Z28).. it struggles to stop and sometimes theres even a burnt smell from all the heat built up. I only had the warped rotor vibrations with the set up I bought the car with. It's got stock calipers btw and they weren't seized when I had them off.
I've already bled my brakes thoroughly and it hasn't helped, the pads do create alot of dust but Im unsure if it's the pads being normal or them doing more work then they should. Around town they work just fine, mushy pedal even after the recent bleed... but they do stop under 55.
I may have a leaky master cylinder by the looks of it, suggestions on a course of action would be much appreciated.