1996 Mazda B2300 battery/alternator

I replaced my battery and alternator in the truck. Everything works and is connected. Truck runs fine. While driving, my battery light sometimes pops on off and the battery level gage drops to a quarter then springs back up. Thruck will still continue to run with no change in sound speed or power while this happens. I pulled the battery and alternator again to have it check. All good, furthermore, I dielctric greesed my connections to the alternator and the battery terminalls are free from corrosion. Any ideas, becuase if there is a problem I cant feel it or find it.