voltage levels

I'm on the road, 2200 miles into a 5000 mile road trip. A 1970 Dart, 318, all new M&H wiring throughout. New stock output alternator, group 24 battery, 70 style regulator. When I start the car in the morning (cold) the ammeter goes to 15 to 30 amps and then comes down to just barely charging in a couple minutes. The voltmeter goes to around 14.4 volts and then after 20 minutes comes down to around 13.5 volts. Is this level of voltage OK??? I don't understand why it starts so high and then comes down. After the car is up to temp, it starts immediately, amps down in 20 seconds, volts around 13.5.