This does not sound like a brake failure at all (based on what you said, and did NOT say).

Somehow, the throttle stuck partly open or you had your foot across both pedals without realizing it. When you slowed down on the exit ramp, you did were not aware that you were fighting the engine until you were almost stopped. That's when you got scared and pumped the brake (you said nothing about the pedal dropping to the floor or being hard as a rock) followed by throwing it into Park and hearing the engine race up. If you lost a vacuum hose or valve to the brake booster, the brakes would have been performing poorly after the incident. The racing engine is the key clue - whatever caused it also caused your "brake failure".

Did you have the cruise control on at highway speed before this happened? Don't forget to check simple things like floor mat bunching under the pedal.