If the pedal is going to the floor as you sit in traffic,the fluid is slipping past the "cup' in the master cyl.
In my past experiences with "fading" stopping power,it has been because of drums that were turned past their safe allowances. It causes them to heat up waaay faster than normal.
You definitely have brake problems that should be looked into. Especially if you have your chilluns in the truck with you.
Marty
