dakota brakes

First of all I would like to say to everyone. I am new to this site and I am looking forward to seeing what is available in here. I have a question to anyone who might know the answer or at least give me a clue as to what to look for. I have a 1991 dodge dakota 4x4 which i cannot get the brakes to bleed up. I have put on new calipers, wheel cylinders, brake lines, master cylinder and a porportioning valve. When the truck is not running i can get a solid petal but when i start the engine the pedal goes to the floor. Anyone who has any ideas would that would be willing to share will be greatly welcomed. thanks.

I'd think there's a vacuum leak somewhere else, as it goes soft once you start it.