complete failure of a wheel sensor will cause the abs light to come one and disable the abs system reverting to standard brakes. proper operation of the typical gm abs system is like this:

when you hit a bump and unload a tire or tires with the brakes applied, that tire(s) decelerates faster causing the abs system to activate and pulse the brake on that tire(s) in an effort to equalize wheel speeds. that is the ratcheting sound and feel you get in the brake pedal. once the wheels resume equal speeds, the brakes return. theres a split second of time for all this to happen and in a tight situation, could be a problem. the logic is that if the wheel is turning, you have at least some control (avoidance) whereas with a sliding tire, you have none. also keep in mind that an unloaded pickup wants to slide the back tires anyway in a panic braking situation. the exception here is on loose gravel or dirt in which a sliding tire causes a buildup of material in front of the tire which may reduce stopping distance but still offers no control for avoidance. the early truck abs systems worked only in the rear. all manufacturers vehicles (especially trucks) with anti-lock brakes exhibit this characteristic to some degree and gm isnt the only one that fields complaints about brakes.

also, the limit speed, where the abs stops functioning, or you couldnt stop at all, is somewhere below 10mph (varies). with speedometer errors, e.g. changing tire size, this limit is also changed depending on which way the speedometer is off. that is why it is critical that the speed input be correct, otherwise the abs may work at too low a speed, or quit working at too high a speed and you may not be able to stop safely.

additionally, larger and heavier tires and wheels increase unsprung weight which has a negative effect on braking and suspension control. an increase of 50% unsprung weight (50lbs. vs. 75lbs.) actually doubles the forces on brakes/springs and shocks. the tires want to keep turning that much more and the shocks have much more to control when you hit a bump. this is different than vehicle loading (sprung weight) which has a less drastic effect on brake and suspension performance. you can load a truck to gvw and still have better brake performance than having it empty with 6" and 35's. you cant make changes to wheels/tires and suspension without changing brakes, or learning to drive a lot differently.

I've been reading alot of stuff on this forum about crappy GM brakes so I hope this explanation helps some...

 

has anyone ever consider replacing the brake booster thats what gives you the assit
your abs work better when you apply more pressure most people feel the pulsesation
and let of sligthly ,thats why you stop longer

 

has anyone ever consider replacing the brake booster thats what gives you the assit
your abs work better when you apply more pressure most people feel the pulsesation
and let of sligthly ,thats why you stop longer

 

It is just typical of the ABS system, I know my truck does it often while braking hard and hitting a bump. I too have nearly rearend people or nearly ran a few red lights because of it. I just brake a lot lot earlier now.