In my experience, this is caused by one of two sensors. The first sensor is called the camshaft position sensor, and the second sensor is called the crank shaft position sensor. Both of these sensors can cause for this trouble. The ony way to really diagnose this is to perform a test drive with a scan tool that has the ability to watch engine control sensors as they operate. This tool allows for you to verify which sensor is causing a signal loss. See if the sensor stops sending its signal, the engine control computer cannot tell what position the engine is and can cause for lack of spark or fuel at that point which will cause a stalling problem. If the dealer is not able to duplicate this problem, it is rather hard to tell which one is that actual cause. You may want to check with them and see if they have test driven this vehicle and duplicated the problem. If so were they able to pick up on signal from either of the sensors? I wish i could tell you the exact one, but there is honestly a chance of either. Feel free to contact me with any questions! Good luck!