I had a similar issue with my tahoe, the brake lights would work only if the pedal where slightly depressed, but if you stepped all the way on the brakes, they wouldnt work. Check to make sure your 3rd brake light is still functioning. If not, you may have a similar issue to mine. I replaced the brake light switch and it did nothing. It is a pain in the ass to get too, even with my skinny ass. Well I unplugged the harness going to the brake light switch and found about 2 good wires out of the 6. The way they had the wires routed from the factory made the wires bend sharply right at the connector. Getting this short harness off was also a large pain in the ass, involving dropping the steering column. Soldered the wires back together as no one had a replacement harness and put er' back in but I did not secure the connector the same way they did from the factory so the wires didnt bend as sharply. That was 3-4 months ago and have had no issues since.