Charging Issue? Computer Issue?

[libers1434]

I have a 2007 GMC Acadia I have owned for almost 5 years. This has been a great car until recently. We replaced the alternator in April while on vacation and while traveling check charging system displayed on the DIS, eventually the battery light came on as well. The Voltemeter would fluctuate between 14 and just below 13. It did eventually get down to around 10. We found the more options we turned on ( the radio, air, full headlights the voltemeter would come back up and stay at about 13. Driving around town once home it would fluctuate most days between 14 and 13. Battery was tested again after a couple weeks and was close to needing replaced so we went a head and replaced. Nothing changed it continued to fluctuate but never sent any messages to the DIS. Last week the Check charging system displayed again and the battery light appeared on my way to work. We load tested alternator in car and was at 14 to 14.5 volts. I then noticed the voltemeter was reading below 13 load tested again and read 11.9. Took Alternator out had bench tested and they said the alternator was good. We worried that it wasn't and replaced anyway. I would like to mention that the transmission was rebuilt in May. Car ran perfectly fine for two days then noticed that if felt like my transmission was slipping or trying to take off in a higher gear because once you got going everything shifted fine. At that same time the check charging system displayed again on the DIS and the battery light came back on. Voltemeter reads just above 13. This has continued for 3 days in a row. Check charging system is constantly on along with the battery light. Transmission sometimes acts up. We know this is not a transmission issue and is related to another underlying issue. Yesterday when I got in the car I noticed my outside external temp for air was reading 102 on a 68 degree day. Just curious as to if anyone has come across a similar situation with an Acadia....Thank you for your time