general problems of the 2001 GMC Sierra

The abs light comes on and the truck does not make a complete stop. The antilock breaks due not work and truck tends to glide. It does this week after week. I am tired of having my truck diagnosed and they can't find the problem. I have come so close to having several accidents because of this antilock breaks that make my breaks go out. I have to shift the truck to park and turn off completely. The break pedal goes down all the way and emergency break does not work either.