I lose all pressure in my brakes when i start the truck

What is your question?

I have replaced my front calipers, lines, master cylinder and booster, (booster and cylinder replaced twice). I have good pressure after bleeding at all four wheels, but as son as the truck starts, i lose all pressure in my break pedal. I can push it all the way to the floor and it slowly depresses back. Any ideas?

How long has your 1998 Ford F-150 had this problem?

About 2 weeks, it started after replacing the calipers.