Brake pedal went to the floor

I backed out of a parking lot then put it in drive started to ease off the brakes and heard a loud bang sound like something broke. Turned back in the parking lot and the brake pedal went to the floor. So, I changed the master cylinder and the brake booster. I've bled it a lot. I know I still have some air in the brake system. When I tried to test drive, I can build up enough pressure to stop. When I turn a sharp right or left the pressure, I built up goes completely out. It does stop the truck but not until it gets almost to the floor.