If my 2003 Silverado's factory radio had the option where the radio volume goes up as the speed/rpms go up, does that mean the vss is right in the factory harness and i can plug the gmos-04 directly from the d3 to the oem harness since metra added this option to the gmos-04?

yes and no. The signal is there in the factory radio harness which allows for factory radios to read it. But the signal is not a standard vss signal it is a data signal which the newer gmos-04's can read and interpret the vss signal.

So if your using a newer gmos-04 you can get the signal right there and it is accurate. I've installed many of them and the vss work perfectly but I've never been able to get the illumination to work through the gmos-o4. For those of you unaware the reason I say "newer" is because the original gmos-04's didn't have a vss signal. I know this for a fact, I've replaced many of them with newer ones to gain vss.