Brake lock-ups at slow speeds

Brake Problem. In addition to what im about to say i also have a supposley bad ABS control unit not a sensor, iv already gone thru that.

Alright so sometimes when i slow down when im already going pretty slow(usually when i first start the car), i feel me brake pedal sorta sink down then pop back up. It feels like it's rolling over something. Actually now that i think of it, it feels like a lock up for only a second and many times. It also happened to me while i was going to park, i went to the spot and while i was slowing down the brakes gave way and i bairly missed the car on the other side.

If anyone has any idea what this has to do with please post it, my idea it that its not gonna be right until i get a new control unit.

Thanks