So, when I drive to work in the morning in bumper to bumper stop and go traffic that barely gets up to 10mph for large stretches, will my TCH run on gas or electric? I really do need to read more about the HSD before I actually get my TCH.

I don't think you'll need to study up. In 10 miles per hour driving you should be on battery most all of the time. Unlike the other post where they get up to 40 (possibly quickly) between lights your ICE won't have to run much in really slow moving traffic (except to charge the battery every once in a while if it's for a long period of slow driving)