I have a '02 SLT Laramie Ram 3500 dually with 5.9L 24V tubo engine and an odd voltage reading problem. When I start the engine the volt meter rises slowly to a little over 14 volts & then slowly falls back down to 11 - 12 volts before rising again to 14 volts. If I have the headlights on, they dim as the volts fall & brighten up as the volt reading rises. It does this several times and usually stabilizes when the engine reaches operating temps. Is this something I should be concerned about or is this normal? What could cause this?