Chris how have you observed this? Someone in the car hitting the pedal while you watch?

On the rears, how hard do you use them? Can you lock the rears? Do you have the stock proportioning valve, or an adjustable?

ONe of the tricks to getting a Z car or the TR8 to stop is to make sure you are actually using the drums in the rear, but taking out the stock proportioning valve, putting in an adjustable, and dialing in rear brake.