I wholeheartedly agree with other members who've suggested perhaps changing your driving style and tracking your mpg's over the course of several fill-ups.
I've had my 'vert for exactly 8 weeks today.
I keep track of my Camaro mileage on mpgtune.com. I'm getting what I'd consider reasonable mpg's with my 2LT manual 6. Compare it with
what I was getting with my 2008 Saturn AURA XR (6cyl, DOHC, 252 HP, 6spd auto w. tap shift which I never used) and my gas mileage with the Camaro is excellent. The last 2 or 3 mpg's on my AURA were on a 600 mile roadtrip. If you go down to the bottom of the page to the earliest fill-ups of my AURA, you'll see that with an auto and less HP, driving in the same manner I do my Camaro, approx. 50% hwy and 50% city / suburbia, my Camaro mileage is better than that of my AURA.
I believe it's probably a combination of things: more fuel-efficient Camaro engine (SIDI), driving style and engine break-in period.
Check out mpgtune.com. It's free to register and it's a simple way to become a little more involved in tracking things involved in the care of your Camaro.