I have a 1968 SS that at an idle the volt meter reads 15-17 volts then when the rpm increases the voltage drops to 13.5 to 14.5. I installed a new alternator, battery is good, and the voltage regulator is only a year old. Everything was fine until I went for a drive in early January and have been trying to figure out what is wrong. Any help will be much appreciated. Thanks in advance.