Brake problem

My truck has a low brake pedal, I have replaced the front brake calipers, rear brake shoes, and still the brake pedal goes to the floor. I have clamped off the two front lines and the rear. That gives me a good firm pedal. If I take the clamp off the rear I lose about an inch of the pedal. I remove the clamp from the left front I lose about another inch of brake pedal. And of course I take the right front off I lose everything again.