1999 Camaro Z28 with 6 Piston CTS-V brakes has started braking weird. When I hit the pedal it stops nears the top almost like there's a kink in it and brakes very weakly almost feels like I'm sliding. If I push harder it brakes really hard and squeals the tires. If I brake hard and pump the brake it feels fine and acts normally but if I'm at speed and don't brake from sometime and go to brake then it starts to act funny. I'm thinking time to swap the Master Cylinder since the car has 225k miles on it. Or should I check something else?