2007 Silverado 1500 Brake Problem

2007 Chevrolet Silverado 1500 V8 5.3 LT
Air Leak in the Booster , Pedal was soft at this point before the repair but still had some braking power.
Since we could hear the air escaping from it, we replaced it.
So replaced it and tested the brakes. same as before but no air leak. we decided to bleed the brakes to see if we could resolve the soft pedal.
2 man system , started at that farthest from the MC,RR RL FR FL used a tube method to bleed and cannot see any evidence of any leaks.
The pedal slowly drops to the floor now after pumping with engine off.
once you turn the truck on the pedal is gone completely with almost no stop to it.. Visually I can see some pressure being applied to the rears but not front but fluid will still spurt out steady at each bleeder. did the master go out or could it be that this vehicle requires a computer bleed procedure?
ABS Failure?