"Which would be correct for my truck?"
If you are interested in correctness, the firewall was originally painted the cab exterior color (same glossiness, too). The inner fenders were a semi-gloss (almost satin) black.
The tailgate was entirely painted the exterior color (letters too).
There is nothing wrong with how you are painting your truck - it is your truck. Since you are not looking for "factory correct" overall, the glossiness of the running boards should suit your tastes.
Maybe someone will know (Denny Graham?) if the running boards were exterior gloss or semigloss from the factory (I did mine as semi-gloss).
Will you be going to "friendly" non-technical shows, or to VCCA type shows?
