Air Brake Wheel Speed Sensor problems of the 1999 Chevrolet Silverado 1500

I have 1999 chevy Silverado 1500 truck. The brakes do not work at low speeds. Two years ago I ran into the back of my own second vehicle, as it was parked in my driveway, when my truck would not stop at speeds lower than 10 mph. I took the truck into the chevy dealer and they fixed the problem for free because of a recall. It is 2 years later, and the truck is doing the same thing again. It will not stop at low speeds. I brought the truck back in and was told that the recall would not cover another inspection. I was also told that the wheel bearing sensor had been cleaned according to the recall and that is was possible corrosion had built up again. I told the dealer that it was unacceptable that every 2 years the breaks just stop working.