driving on the highway for about 5 miles. got off and stopped at a red light, . i let go of the brake pedal and noticed the dashboard brake light had come on. made a turn and pressed the brakes and got very little response. the pedal felt exactly like a car that has not been started and put in neutral. the brake pedal was hard. i pushed with a lot of force to get the car to stop. i then pushed the gas because i had a feeling that something was just off and it worked. the light went off and the brakes worked. after i tried going slow and the brakes went out again. seemed like when i pushed the gas the brakes worked but when i roll at a slow speed they failed. hope this isnt confusing i tried to explain best as i could. any help is appreciated. thanks.

 

I know this is late but you might have a failed belt driven vacuum pump. It should put out a steady 19 to 20 in of vacuum.