I also am having this problem on my 1998 silverado k1500. i recently replaced the brake booster and after finishing i realized that my brake light were still on when the truck was turned off. i was told that it might be the stop light switch on the back of the the brake pedal. so i replaced it with an acdelco part it was defective and created another problem which was i couldnt shift out of park...so i replace it again with a BWD part and my lights are still on but i can shift. i ve taken it to a mechanic and he can frigure it out either so any help would be apprecatied.