The brakes on my 1999 chevy suburban have a hard pedal but as I continue pressing it goes slowly to the floor. After the dealer worked on it the problem was worse. The front rotors and calipers were replaced and the rear drums were inspected. There are no leaks, I am not loosing any brake fluid. Bleeding the brakes does not show any air in the lines. The truck stops quite well from high speed. In traffic when I use the brakes to slow down with constant pedal pressure over a longer time period the pedal goes to the floor and the red dash light comes on. If I pump the brakes I can stop and the brake light goes off. When the master cylinder was replaced it made no difference. Could I have gotten a bad replacement master cylinder? What is the red brake light senceing?