Brakes Grab...Then Release...?

[rico05]

So my new chassis seems to have an odd issue. Sometimes (mostly first thing in the morning) my brakes will grab then release, the car will drop revvs and stutter, then go back to normal. It is like all vacuum is gone. I have done the tests in the FSM for the booster, and it is fine. Any other thoughts? My old car did this like once or twice in 4 years, and only in extreme cold. Could it be the check valve in the vac line for the booster?

It only happens at low speed and only when the car is totally cold (ie when I al leaving the apartment parking lot first thing in the morning).