Voltage Spike

Driving home from work and I notice my headlights get brighter. I see the voltage gauge spike up to 18v and my ABS light comes on. Truck ran fine. Spiked like 3-4 times during the 20 mile trip. Replaced the alternator a few months ago with a Duralast Gold from Autozone. Any ideas?

I need to get people from the airport tomorrow and a kid to college on Friday. FML

Thanks!