You'll need a VIN, $5 and an email account to tell definitively. Compnine - http://www.compnine.com/vid.php

Screenshot - (your VIN will appear above the vehicle model)



I really wouldn't worry about it, tbh.

Edit: I only checked for '03 down for other members when I gave the vin checks away. So, I don't know for sure that 04+ will denote GT1/GT2.