Hi there. I just read your querry and I can tell you that there is a VN GTS. I have one as well.
The other person who stated that the VP is the first GTS is kinda true. It is true to the point that it is the first VP HSV GTS. The VN GTS is not an HSV.
The VN GTS Commodore is a 3.8 litre V6 that mainly came out as a 5 speed manual (there are automatic versions available, though not as collectable). but the difference with the GTS compared to the rest of the V6 VN line up is that the GTS has full SS running gear and trimming. It should also have the Commodore GTS badging on the dash board on the passenger side.
From my understanding there were only 1500 produced, with only 500 making it to New Zealand. This makes it a very collectable vehicle.....considering that there is not alot of VNs left in good condition on the roads.
And to answer your querry about your car being a VN: The VN model commodore replaced the VL in September 1989 and was manufactured until March 1992 with the release of the VP (and this also includes the VP HSV GTS)
I hope that this has provided you with some knowledge. I was very suprised when i picked up my GTS. I am now looking at pulling mine off the road and giving it a rebuild
Good luck with yours mate