2006 Dodge Truck Voltage Regulation

New probelm: Often on (every day or so) it appears that the alternator is not charging, but then the next time you check it, it is charging fine and maintaining adeqoute charge.

Have had it in to local shop, they indicate that alternator is putting out 30 amps some of the time, and 150 amps at other times. Additionally they said I could replace the alternator but that might not fix it. Is the regulator internal, external Where?

Truck is a 2006 Dodge 3500 Diesel