2003 VR6 Died in Traffic

My wife was driving our 2003, VR6 with automatic, 40,000 miles to work in traffic last week when it suddenly hesitated a few times and died. Plenty of battery power to start the engine, however, it wouldn't fire. Had it towed to a local VW dealership where they weren't able to locate a problem. No error code showed up which seemed strange to me. They kept it for 5 days trying to duplicate the problem, but weren't successful. I've been driving the car for the last week with no problems. Any ideas or has anyone experienced the same problem?