Brake issues

[nhtc33d]

I am have a issue with soft pedal in my project. Replaced entire brake system except for rear brake hose. New disc/drum setup with manual m/c with prop valve. Bench bled m/c, gravity bled system 2x did the pump and hold 2x went through 3 bottles of fluid but still have soft pedal. BUT if i pump it up quicky and dont release the brake pedal completely it stays firm. Just keeping the pedal pushed down 1/4 inch keeps the brakes up. Could there still be air in the lines or do you think there is other problems?