Need advice

I have a 1998 S10 2.2L 2WD...I couple of months ago the voltage meter was starting to dip toward the 9. And while I was driving the cluster gauges would light up and my truck would stall. I would sit for a few minutes and it would start right up. So I took my truck to my mechanic and he replaced the alternator and for kicks I had the battery changed also. All was well for a couple of months, when I notice the the voltage meter started doing its little dip again so I took it to Autozone to get my alt and bat tested. Everything was fine. So a couple of days later while driving to work; the instrument cluster gauges light up again and the check engine light and security light stay on. So I take it to a shop and the pull a P1632 code. What was basically was told to me is my baby thinks I am stealing her. Can anyone enlighten me on how all this ties together?