i have a 1980 c60 chevy truck with brake problems on 1990 Chevrolet 2500 Pickup

i have changed master cylinder and brake booster i have adjusted all brake adjusters on all wheels i have bleed brakes several times. first time u push brake pedal u get very little brakes 2nd time u get half brake pedal 3rd time u get full brake pedal. what is wrong how can i fix this?

Asked by for the 1990 Chevrolet 2500 Pickup
i just bought one of the same year and model and it is doing the same thing, haven't got to work on it yet but i was told it was the adjuster inside the drum was froze up and was letting the slave cylinder over extend, i'm going to try adjustment first, may have to rebuild the slave cylinder or new shoes!