[Ridenour]

Sounds like a faulty sensor. The sensor may just be popping in / out from the force of acceleration and braking, and since it doesn't recieve a signal it disables trac control. Or it could be mis-calibrated and think that you're hitting something rough (like deep slush) or something and be disabling it. Either way, it sounds like you may end up needing a new hub sensor - or just try cleaning all of them.