Check out Dream Car Rentals:
dreamcarrentals.com
I flew in and took a GTS out for the day before I bought mine, to fully fathom what I was getting into. Big mistake, I almost didn't buy one.
Cars are neglected to the extreme. My car (96 GTS with around 20K) was way down on power and I attributed it to the elevation in reference to where I do my driving, a difference of 8000 feet , losing a few % of power at each 1000 feet, I figure I was down a 100 horse. Lack of brakes and missing suspension parts added back the excitement of the lost power however.
There is another rental shop off the strip that comes better recommended, and naturally for more money, that specializes in Vettes, RentAVette, I believe is the name.
Of course, if it's an SRT, go to where is cheap and be the first to hound on it!!