1996 Chevy Astro charging system fluctuates?

The needle on the electrical gauge usually sits about one or two "needle widths" to the left of center. When I first start the van the needle will be centered or even one needle width to charging side. After driving for awhile, it will change to the discharge side, but only slightly. Running heater, lights etc, doesn't change the needle position. Should I be worried? What should I do? Bothers me to see it in the discharge side, even if only slightly. Bought the van used about 8K miles ago and has been this way since. Thanks