So if I read correctly, the truck has since started and is now running. You checked the battery voltage and it is now 6.3V (not running) and 8V charging (running).
Just to be on the safe side, I would take the truck or battery to your local parts store and have them check it with their load tester.
If the starting problem happens again, you can eliminate the battery.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."