2005 Dodge Sprinter Dodge Sprinter engine stalls every summ

Engine Performance problem
2005 Dodge Sprinter Two Wheel Drive Automatic 28000 miles

2005 Dodge Sprinter 5 cyclinder diesel: Ever since we purchased this vehicle in the summer of 2005, it has stalled numerous times every summer. Everytime we take it to the dealership, they have been unable to duplicate, trouble-shoot, or determine what is the problem with the vehicle (engine stalling) suddenly shutting down during normal operation. It happens most of the time when the vehicle is in motion, traveling between 20-40 mph. They suspect too many keys attached to the key in the ignition which may inadvertently turn the ignition key counter-clockwise. But we only use the key with nothing attached to it. And it's not the diesel fuel. Again, this only occurs during the hot summer season. The rest of the year, the vehicle operates well. They have replaced the radiator, and I don't know if this is associated to the problem.