Brake pedal goes to the floor?

2 months ago, I changed the pitman arm, tie rod ends, lowering shackles, and brake pads. After changing the pads, the trucks brake didn't work. So, I bled the brakes, and no difference. So, I figured it was the master cylinder and I changed it and bled everything again. Still spongy brakes. After that I changed the front Calipers and bled the brake system. Still spongy brakes. I then changed the brake booster, and pedal still goes to the floor. And I noticed when bleeding the brakes I wasn't getting fluid to the rear brakes. So, I changed both wheel cylinders and all the soft brake lines in the front and back. Fluid came to the back again, but the pedal was still soft. And I noticed brake fluid on the master cylinder and brake booster where the push rod is, so I replaced both parts again. Bled the brakes maybe 20 times total in the last 2 months and still a spongy brake pedal. I did an ABS bypass because I was told there could be air in the ABS system and still, I have a spongy brake, slow return and pedal goes to floor. I do build pressure when the truck is turned off but as soon as I start the truck, all the pressure disappears, and pedal goes to floor. At this point I am stumped. What else can I do or try?