headlight dimming/voltmeter jumping

[Deezel4x4]

I posted a problem I have been having with my truck a while back,and all the responses were checked and none of them were the problem,sometimes(few times a week) my headlights will flicker and my voltmeter will drop a little along with the headlights and dashlights. It is aaa totally random thing,it does it under any degree of weather. It does not have a rhythm like the grid heater and it will do it sometimes for the whole length of a 3-4 hour trip and then it wont do it for a week. I have changed the batteries and have cleaned the terminals and made sure they are tight ,I have checked all connections,is my alternator taking a dump on me or what?rpms of the motor do not affect it when it is doing its flicker thang either

 

[illflem]

Could be that the PCM is bad and is telling the grid heaters to go on when they shouldn't be. Try putting a voltmeter to the heaters when the voltage is acting up or disconnect the wires at the intake, protect from grounding, and see if the problem stops. You should be able to get away with no grid heaters in FL.