03 Dodge Ram, 2500HD, check gauges light coming on

Ive got an 03 Dodge 2500 HD Pick-up with the 300 HO Cummins motor in it, its a Manual transmission, and Ive got about 65,500 miles on it.
Ive been having this issue of my check gauges light coming on for about the last 6-8 months now and can only think of one thing causing the problem. I think the voltage regulator is going out, or is having serious issues causing intermittent failure. The reason for this is that I can sit behind the steering wheel and watch the volt meter move extensively weather at an idle or just traveling down the road at 2k RPM's and when it gets to a certain point either above or below the 14 volt mark, the gauges light comes on.
Ive had it in to the dealer that I purchased the truck from and after their testing, said I needed a new instrument cluster. I've had the battery's replaced, and replaced the alternator but still Ive got the same problem, the volt meter will go to about 14.8 volts and light the check gauges light. Also the 4x4 indicator will flash on periodically which I believe to be related to this problem.
I'm wondering, just exactly, where is the voltage regulator on the truck, so that I can maybe replace it if I need to, or is it internal with the Alternator? Or is this really my problem? Thanks for your help guys
Snocat,
Spring Creek NV