Brake pedal staying part way down?

[BigSky71]

I have re-assembled my truck [71 2wd stock disk brakes] and have a nagging problem with the brake system. Everything is new except the brake pedal assembly and the prop valve. When I press on the brakes the pedal stays down part way, say 3". This keeps the brakes slightly applied, enough that the truck can't be rolled around the garage without lifting on the pedal each time. Does anyone know why my pedal would not want to return to the full and upright position? I have bleed the brakes, and the reservoir is full fwiw... thanks!