1997 Dodge Caravan Brakes, stopping

The Master Cylander was recently replaced. The brakes do not seem to react quickly enough, especially braking in reverse. Also when stopping quicky, the brake peddle seams hard at first then lets go almost to floor. The engine seams to strangely rev or decrease rev with braking.

And lastly there is a hissing noise coming from the area of the master cylander when the brakes are applied!

Thanks, Al