1999 Chev Silverado - Loss of all electrical power

I have a 1999 Chevrolet Silverado K1500. Intermittently it will loose all electrical power while I am driving down the road. (Everything on the dash goes out just like the battery was disconnected.) After a short period of time, 15 seconds or so, all power returns and the truck can be restarted. Sometimes it will happen only once in a trip, other times more. Could this be an ignition switch problem? All electrical connections are clean and tight. :)