Is my booster bad?

Hi Guys. I have a 72 dart with stock power disk brakes. My problem is twofold.

When I brake at a light I notice that if I press hard on the peddle while stopped the idle lopes and gets rough as if the engine has sprung a vacuum leak. If I ease off the pedal the idle turns normal again.

Second, I had to brake hard on the freeway the other day and everything was working great until I had to really step on it. It seems once I passed a point in the pedal travel the brakes became rock hard and would not give me extra stopping force. Scared the $*#@ out of me.

Thoughts??

Thanks