I have a 99 Silverado 5.3L motor and I am beginning to have voltage problems with the truck. Just today my voltage meter dropped down to around 12 volts while I was driving. I turned the truck off restarted it and the meter read "14 volts" again....5 minutes later it dropped back down again. What could be causing this problem?

Check out this thread. (http://www.automotiveforums.com/vbulletin/showthread.php?t=359344&highlight=voltage)
This deals with your exact issue and has a solution to your problem. Another thread was started two days ago on this same issue. I, personaly, have found that doing a search in the forum first can answer many questions. This helps in producing redundant threads.

Hope that the thread above helps you out.
Jake