I have a 2007 base with the Z51 package and when I got it insured my agent puts in the VIN and it comes back as a Grand Sport. I thought that the Grand Sport came after 2007? Is the Grand Sport the same as a Z51?
The Z51 claim to fame was the performance handling package and possibly the Mag ride option. In 2008 the engine was changed to the LS3 for a 30 hp bump up. The GS in 2010 was the replacement for the Z51 but it was not the same. The GS is a widebody design (fenders) and there was a 4LT trim option as well that I'm not sure was available on earlier models of the C6. Not sure why your Vin comes up as a GS.