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It sounds like this isn't really a solvable problem. He did everything he can do to make sure there isn't a physical problem. (Had the alternator checked, had the battery checked) In my opinion, it is normal for the alternator output to decrease when the cooling fans kick on. After all, now your alternator is powering two additional motors.
I empathize because the Vettes have so much more detailed information than most cars do, and monitoring your DIC is addictive. Still I don't think there is an issue.
The guy who said that he could see his radio lights flicker had an issue, but if the only way you can tell is through the guage; probably not an issue.
I'm gonna try the Big 3 because I have some 2ga. already sitting in my garage....but I'm starting to think like some of ya'll and just maybe askeing too much from a 100amp alt! Thanks for all the ideas gents, I really do want to thank you.