Bad alternator?

Well, my alternator and battery both checked out OK. I raised my idle a little to keep it from dying while in Drive. To keep it from dying I have it idling at about 650-700 rpm while in Drive, which means it idles at around 800 while in Neutral.

I hooked up a voltmeter to the battery and while idling in Neutral the voltage reads around 14.3 volts (with lights on). When I idle in Drive the voltmeter reads about 13 volts on the battery and my ammeter goes toward the "D" (Discharging). Once I switch it back to Neutral the voltage slowly goes back to 14.3 volts.

Is this drop in voltage while at the lower rpm normal or do I have an issue with the voltage regulator or something else? Thanks!