volt meter fluctuation

I have a 93 Silverado 4x4. I had a battery problem, so I replaced the battery. I also noticed that the battery cables were bad, so they were replaced as was the alternator.
Now, my volt guage is pegging out at 19 volts and the battery light comes on when this happens. When this happens at night, everything electrical seems to brighten and dim.

Any suggestions? Bad alternator?

Sounds like you are having similar issues as this guy: http://www.automotiveforums.com/vbulletin/showthread.php?t=470846