I had the same problem for the first two months, where I didn't think the tempurature was cool enough. Finnally the A/C went out of the freeway. It started blowing hot air, with the clutch engaged. Luckily we were just getting off the freeway and the dealership where I bought it from was on the corner of the freeway exit.
Took it in, the mechanic basically said, he's noticed that out of the factory GTO's happen to have lower freeon levels then it should be.
He filled my A/C up, injected a dye to check for leaks. No leaks were found. Haven't had a problem since.
Purchased my car on 7/7/06
Took it in for an A/C check-up in september 2006
Haven't had a problem since, I actually have to turn it off from time to time while Im driving. Even today, with scorching heat, it gets too cold in my car. My car is black too, so you know it gets hot.
Take it in, bitch and complain. They'll fill it up for you.