Ah, OK, now I'm awake and I understand. I looked at a GM RPO list and the different VSS RPO's are either D8_ (where _ = a letter A through N) or D9_ (where _ = a letter A through E). That should be listed on the SPID label on the trunk lid. Makes sense that there would be 3 of them, as you'd need a different one for each axle ratio (Duh!).