2017 Silverado 3500HD Low Voltage Issue

[airboss20]

I Have a Silverado 3500HD with the 6.0L Gas engine. I have a low voltage situation that I don't believe to be "normal". The dash gauge shows normal 13.8V upon startup, then a few minutes it drops to about 10V. The needle settles just above the lower limit for "normal". I know that the user manual and manufacturer specifications describe this as a normal condition, and the charging system will lower the voltage to extend the battery voltage.

Here's the rub. A couple weeks ago, I took the truck on a 5 hour road trip. I noticed the needle drop during this trip. I left the vehicle and did what I had needed to do. When I returned, the truck started normally and operated well for the trip home. I stopped for gas just before parking the truck for the night. After filling, the battery didn't have sufficient charge to start the vehicle. I had the battery and alternator tested separate by removing each component and taking to a test facility. Both were fine on the bench.

Why did I lose charge on the trip? Why do I never see the voltage gauge return closer to 14 volts? Anyone have experience with a similar condition?

[Blue Bowtie]

Is the instrument panel indicating the correct voltage compared to an actual voltmeter connected for comparison? We know that the "instruments" stuck into the dash are no longer actually instruments, but stepper motors controlled by the cluster logic and PCM/BCM.

It could be even worse than the gauge is indicating.