Auto Mechanic Question

[Reverb]

My Tahoe has been acting " funny" lately.

When I'm idling in a parking spot, the engine seems to lose power for a second,ever so slightly, and then corrects itself. All the while,The volt meter hoovers around 14, the goes down to 12.

Whats up with that ?? Batteries fairly new, I'd say 18 months. I do drive 60 k a year.

Thanks for any input...