88 Gmc Brake PRoblems

I have a 1988 Gmc Sierra 1500, and my brakes are soft(goes to the floor with little to no resistance). This is after i replaced the brake booster , and the master cylinder. Anyone have any ideas I don't know what to do next already put 200$ worth of parts on it , which didn't fix the problems , and
yes I've bled the brakes on all 4 lines , and the on the ABS system. and its coming out
with no air in the lines!

first, what is the history of this problem? when did you notice a problem and what all have you done to diagnose and repair this truck?

when you say you can press the pedal all the way down, where does the truck stop at? Does it still stop near the top or middle or does it take you pressing the pedal all the way down before it starts to stop? When you come to a complete stop, where does it start to roll again as you let off the pedal? is it right at the bottom, half way up or 3/4 to all the way to the top before the truck starts rolling again?

ABS can cause a low pedal feel. rear brakes out of adjustment, master cylinder, the wrong disc pad materials may cause you to press harder on the pedal to get the braking to stop the truck.

the slave cylinders were leaking so we replaced them , then i know we had to bleed them then. but then he bled them and still had light brakes , I have to push them all the way to the floor just to stop and if i unplug the brake booster i have tight brakes like manual brakes.

make sure you bled all the air out of the lines. Did you readjust the rear brake shoes when you were done? If you start and drive your vehicle in your driveway, after you stop and push the pedal all the way down where on the pedal return does the truck start to roll? As you let the brake pedal up from the floor, how far up does it go before the truck starts to roll again? (on flat ground of course, if you're on a hill or something you'll have to try it somewhere flat)

yes, pumping the brakes until the vacuum is gone will make the brake pedal harder to push but how high is the pedal stopping? it good and hard very close to the top? or does it still go way down?