Bingo. Fords have what they call a smart charging system. The battery does not need 14+ volts all the time. The alternator is being efficient, stop taking your cars to the dealer for this lol.That's what a voltage regulator does. PCM will determine how much the alternator should output. It'll vary depending on load. Once the battery is fully charged, there's no reason to maintain 13.5V+. Your cars run off a 12V system. The excess voltage is to restore the battery after loads have drained it.
My digital gauges indicate an average of 12.1 volts coming from the alt jumps to 13 but drops back down slowly. Is anyone else having this problem?