Diesel Bombers - Overcharging

I have been having an issue with my charging system on my 2002 cummins. The system seems to charge normally most of the time... but when I hit the bypass and exceed 70mph, my voltimeter pegs 18 volts. I have been pulling over and turning the truck off to reset the internal voltage regulator in the pcm. The gague is correct and verified with my ohmmeter. I have checked all my grounds and checked for open short in wires, have been unable to put my finger on the issue. I am contemplating going to an external voltage regulator? The PCM is operating fine otherwise and I can't rationalize spending the money for a new PCM when my problem is only charging. Anyone know anything that I could try, I also recently wired up quadzilla on my truck. The quadzilla was for a 99, therefore I had to make some modifications... does anyone know whether or not that would affect the charging system via the PCM. I wired it just like a 2002 would be, and to my knowledge the boxes are all the same.