Stiff brake pedal

Okay, well my brake pedal gets extremely stiff and my car takes a hell of a lot longer to slow down when I am slowing down from higher speeds like over 80mph. It kind of feels like there is no power brakes. I just put on new front brembo drilled/slotted rotors and ceramic pads. Is the stiffness in the brake pedal just abs at work or, is there a possible problem. I don't recall noticing this before. Also sometimes the pedal goes down easily at first then about halfway down gets real stiff. Thank you for any help.