Digital gauges anyone? Question about the voltmeter.

[Happyfunballs]

I have a Dakota Digital setup in my 67 and I'd like to know if anyone's voltmeter fluctuates. Mine will go from 14.5 (above 1400 rpm) to 10.6 under load at idle. Seems to me a huge swing in voltage. I recently rebuilt my 10si alternator and upgraded it with 140amp(three wire) innards and I've tried a red top and blue top optima with the same results. 4ga monster cable ground wire from frame/body/engine and I'm convinced(based on numerous readings) it can't be a faulty ground. It never stalls and it seems to run fine, but honestly, it's buggin me.