I recently bought a 2001 Chevy Durmax. The alternator is discharging at about 2,000 Rpm. It charges fine while the truck is at an idol or you are driving along. If you get into the accelerator and the RPM s come up, then the volt meter drops down to around 12 or so and the headlights dim if it is at night. Strangest thing I have ever seen. I would appreciate some advice on where to begin. The alternator tests fine as do the batteries.
Thanks for the help.