Cuda overcharging? Please help...

My voltage gauge in my cuda is telling me it's getting about 14volts at idle, but whenever I give it gas it makes it's way up to about 18volts. It's a brand new alternator and I've gone through 4 voltage regulators trying to get this thing to charge right. Any idea what could be causing this? If anyone could throw some ideas my way as to what the problem could be it would be great. Thanks guys