1995 GMC C1500 Battery light and voltage surge

First, I recently had a lot of work done to this truck. My dealership replaced the intake gasket (due to a coolant leak). After this was done, they found the need to replace the plugs, wires, distributor, and rotor. It has been running good since.

But now, about a week later, the battery light flickers on and off in a very spiratic manner. I also noticed this morning on my commute to work that every time the battery light came on, my headlights got significantly brighter. The voltage stayed steady at about 13 volts. For the previous few days the voltage stayed at about 14 volts. But yesterday after an hour drive home, the voltage dropped to around 10. (But it was back up to 13 this morning.

Do I just need a new battery? Could the electrical parts swap have caused this problem? Alternator?