1998 GMC Sierra brake lights don't work

My brake light will not work. The third light works. i replaced the switch under the dash that is directly on the brake pedal. i have checked all the bulbs by changing them to the blinker location and both filaments work. i have chased wires from the taillights to the front, but once the go up i loose track of them. I also swapped the ignition relay and the stop/hazard relays and nothing. All fuses are good i checked them with a multimeter. I even went a little farther and shook the blinker lever and hazard switch to see if maybe they weren't all the way off. after that i am all out of clues. thanks