1998 Chevy Astro Battery and Alternator

The other day my battery light came on and I noticed by battery voltage sitting halfway between 9 and 14 which started me because it's been sitting just below 14 this entire past year. I put in a new battery in April of 2008. Upon checking the voltage it was determined that I needed a new alternator. I purchased one from O'Reillys, however within 1 week I am having more problems - it's still sitting between 9 and 14 and doesn't want to start immediately. At first I get just dash board lights, then I let it sit about 20 seconds then it starts. I had battery tested and replaced then had O'Reillys check alternator - they said it was a bad alternator. We exchanged it out and even now with a new battery and a new alternator (which by the way was tested and it passed) we still can not get above the half way point between 9 and 14. With the car running it is only putting out 12.8 when it should be high 13's. Any ideas? Please help