Silverado voltage drop

[arctictwist]

First, background. Truck has had the big 3 upgrade and an optima yellow top for 4.5 yrs. alternator is stock. Stereo isnt crazy, just a 1200 watt sub and 360 w speaker amp. My voltage always read around 12 but when i did the big 3 it shot up to a little over 14.

 

So yesterday im in traffic driving to work and i start getting abs and stabilitrack warnings. And i noticed the voltage was dropping. It dipped quick to the 11.5 line and then went back up a little. Maybe 12.5/13? I turned off everything and continued to work. The voltage stayed there.

 

A few hours later i started it up. No problem. Battery charged right up to ~14.4 so i turned it off. Morning comes and its time to go home. Again starts right up, charges right up, everythint is fine till i get off the highway. As soon as i stop at the light it happens. I stop in the store for a few minutes. Come out and again starts and charges right up. Happens again a couple minutes down the road. Then it hit me, it starts when i get to 210 degrees.

 

So today i drive to the gym, no problems until i hit 210.

 

So logically im thinking the radiator fans are causing the voltage drop.

 

How can i further diagnose, is my logic sound or am i totally off on the possible cause? Thanks.

 

Ken