Overcharging

1994 Dodge grand caravan sport. 126,000 miles. Automatic. With no problems for 2 years previous my van started overcharging. The dash showed 18 volts and the battery 18.45 volts with a meter. I figured my alternator or voltage regulator went out. I changed the alternator and battery and still showed 18 volts. I've had the battery and alternator tested at the local auto parts store and they test good. Is the voltage regulator inside the alternator on this model and year van? What else can I check? Please help? Thanks in advance.