its posible your brake power booster is not getting enough vaccum to it or its defective. one way to see if its working is shut the car off, apply the brakes 3 or 4 times to bleed the vacuum in the booster off. then with your foot pushing on the pedal start the car, the pedal should drop another 1/2-1". if it drops there might still be another issue but its probably getting enough vacuum. also if your car is idling up a hill your idle may be set to high