01' Chevy Camero Z28. Car's Battery gage bounces up & Down while steadily going up?

The car is a 2001 Chevy Camero Z28 with about 64,000 miles on it and has been well maintained. This problem happens intermitenly and only when Excelerating or is in gear and moving. The battery gage will bounce up and down slightly while steadily increasing. Also when it does this the headlights and inside lighting flicker with the bouncing of the battery gage. Once I put the car into neutral and coast or Idle the battery gage returns to normal, as do the lights. Any ideas what might be causing this????