Crankshaft Position Sensor problems of the 1999 Mercedes Benz M Class

My 1999 mercedes ml320 stalled in traffic on the interstate. I had it towed to the dealer who replaced the crankshaft position sensor which showed a marginal problem. We picked up the car and brought to the attention of the manager that the "check engine" was illuminated. He said that was because there were some plugs misfiring, but that would have no bearing on the car stalling. The next day, the car stalled in traffic and was again towed to the dealer. They can find nothing wrong with the car and say it runs like a top. We refused to take the car until the problem was resolved so it was decided that a technician would drive the car until it stalled again. That has been going on for one week with no stalling. We are at a loss as to how to procede with this issue. We do not feel it is safe to drive the car because we fear it will stop again in traffic and cause an accident and/or deaths.