When is last time you flushed all brake fluids out..?? Needs done every 2yrs.. no exceptions.. maybe po, used wrong type.. start there its the ch cheapest.. look in brake reservoir and tell us the color ?.. it should be almost lear.. then start checking a/p.. when was it last maintenance .? Look on a/p brake drum and see if discolored.. they are not related but still need maintenance.. . then look for good grounds... they always need cleaning.. check abs, sensors.. check their connections they get corroded.. blow air though front ads sensor and rotor and blow the rust out.. some here have had rust get in the way of sensor reading the sensor ring.. on rotor.. that is cheapest thing.. use mask.. brake dust is nasty.. do you have special scan tool? Most don't read abs codes.. good luck and let us know what you did and maybe better members then me will help you..
2000 southwind storm, workhorse custom chassis with 7.4l vortec