el camino brakes

1978 el camino power front disc brakes drum rear stock . have replaced front rotors, calipers, second set of pads(delco this time),master cylinder ,rear shoes and wheel cylinders . have blown out lines , installed one man self bleeders . have had them pressure bled, have bled them more times than i would like to talk about. pedal comes up after bleed them ,when you drive car pedal slowly goes to floor and car slowly stops.you cannot slide the tires.all lines are open have since put new master cyl. on . still no brakes.

No signs of leaks anywhere? Only thing I can think of is its possible you have a defective master cylinder.

I had a similar problem with my 79' ElCamino.
The car wouldn't stop if Superman was pushing on the brake pedal.
I tried adjusting the brakes and found out it was the power booster.
Fixed the problem right away.