if rotors are new or you resurfaced them..then let the damn brakes break in first..since you experience this in slow speed i'm thinking (5mph) that is common until the surface of the rotor becomes slippery....give it a week and see if it does it if it still does....try going past 70mph and step on the breaks...if there is any sort of vibration under your foot or if the steering wheel is vibrating then you have to resurface the rotors again.......the vibration under foot test can only be done on NON ABS cars since on those you feel a vibration either way and its normal.