Erratic Flickering of all electric devices (headlights, dashlights, AC)

I experience erratic flickering on headlights, dash lights, millage display, radio display, and even hear the AC fan speed varying up and down irrespective of the set fan speed. I have changes the alternator, the battery, and the battery terminals but the problem persists. I had a shorted spark plug wire. I replaced all wires (an expensive set for the SS 5.7L model)and changes the spark plugs. The problem was very severe before I changes the worn out wire but it continues despite all the replacements. I have consulted 2 car electricians but that didn't get me any where. Please help.