Truck Repair: charging system

Question
I have a 2005 Chevy Silverado. I had a “charging system failure” message appear and noticed the voltage reading was low. I went to AutoZone and the ran a diagnostics. They told me I had a bad battery but my alternator and starter was fine. I put on a new battery. A few days later- another “charging system failure” and that battery died. I had a new alternator put on and the following day me new battery appeared low (although the charging system message had not appeared). I went back to AutoZone and they ran a diagnostics and told me it indicated that the new battery was “bad”. They put on a new battery and sent me on my way. Now, it appears the 2nd new battery is creeping below 14V just like the other ones did before they eventually wend bad. Im a bit scared to drive it and really can’t just keep changing parts. Outside a new battery and alternator- any advice before I simply take it to a high priced shop for a more through diagnostics? Thanks so much

Answer
I don't work on cars so I can't really help you, however I have a similar experience with my jeep you might check if you look at the large wire coming off your alternator you might see a smaller 18 gauge wire come off with it. If possible follow that it will probably lead to a computer. My jeep did that and one of the likely problems they say is that computer controls turning the alternator on and off. I got lucky and those wires are shot. but could be a possibility. Sorry can't help you more I work on big trucks.