Just to finish this off.
Got my truck back today - along with a very interesting conversation about fuel, flash point, computer controlled ignition, and gas issues in less active stations ... etc.
Anyway, the consensus is, probably bad gas, or low flash point fuel processed and sold at an out of the way station. Which actually happened ... we were in an off-road area and needed gas, so against my normal choices, bought gas at a "mom and pop" station - which I almost never do.
But, nothing shows anywhere in the codes, no bent lines, no plugged anything. So, for now, I'm going along with the "bad gas" or "low flash point" thoughts.
The mechanic (two of them) went over everything, and then explained everything they did to trouble-shoot, including explaining how the computer checks all systems -- extremely enlightening experience. So, anyone in the San Antonio area, with truck needs, VARA Chevrolet does a very good job ... and it's kinda refreshing to find that - good luck for us - 1500 miles from home.
So, got it back today, runs like it should ... no troubles. Will get on the road tomorrow toward Death Valley again.