Intermittent failure of electrical system

When driving (at any speed), the elctrical system intermittently cuts out, and on the last go-around, just failed. When I say failed, I mean no power anywhere. When the intermittancy happens, the volt meter on the dash fluxuates, and the truck obviously looses power. No warning light(s) are shown and there are no error codes. If it recovers from an intermittent, I notice that the voltage is down around 9-10 volts and dumps signifficantly if the headlights are turn on (I don't expect the dash voltmeter to be that accurate) and stays there. Normal voltage before intermittancy starts is around 13 volts. The last time this happened, it just quit. Opened the hood, saw nothing unusual (cursory inspection) and noticed that the hood aux light was lit. Went back to start the truck and it started right away. Again the voltage was down and I noticed the the clock had reset, telling me that there was a complete loss of voltage. No blown fuses are found. Went to PEP Boys and they found nothing (I suspect they only checked for an error code). Any ideas where to start look for this problems resolution? Any help is greatly appreciated. Thank you in avance.