Well, I changed my CPU cooler last Wednesday night. I have not had a crash since. Thanks again for the tip, WolfRaven.
After the change, I noticed that the fans were barely moving. Then I noticed that the smart fan control in the Gigabyte app center was set to quiet. I remember setting that when I built the computer 4 months ago, and then forgot about it. So I changed it to performance and they did spin a little faster. Before the cooler change, in quiet mode the CPU temps would be between mid 40's and mid 50's. Of course, with the fans running low, who know how hot other parts on the MB were getting? After the cooler change, in performance mode, the CPU stays in the low 20's. The system case and GPU were also running cooler. I probably didn't need the cooler change if I had remembered about the fan speeds in the bios, but it's nice having a high performance cooler. Maybe I'll try overclocking.
So yeah, I can see the app center causing a problem if it is not set up correctly. There could be fan speed or overclocking or voltage setting issues. With the app center removed, I assume all your fans are running full speed, so I doubt temperature will be an issue.