I would Like To Know Why My Explorer Shuts Down While Driving

One Day In The Afternoon Air Temp Was 107 Was Driving My Auot When It Decided To Shut Off Put In Neutral Restared Motor Later Died Again With Truck Parked I Can Start It And It Won't Die I Am Affraid To Drive It On The Road I Recently Replced The Alternator With A Used One Seems To Be Charging Ok Checked Alt Output 13 Volts