Are stock brakes just bad???
I was traveling at about 100+ on my 3rd run between lights when I really had to jump on the brakes hard and a loud shuddering came through the car???
Any ideas??

Pads and rotors only have 20K on them. All stock brakes...

 

If you were running high speed light to light and stopping hard or even just semi hard, you were heating up those brakes far past any normal operation. The stock brakes aren't designed for that kind of frequent use without extended cooling periods. You're lucky they didn't fail you in a pinch.

Driving like that on a track you should upgrade your braking system. Driving like that on the road is irresponsible and you should stop taking chances.