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This is one of the best posts I've seen on this forum..it's too informative..thanks.
Just check out what would your code scanner say and try resetting the PCM, your problem may be identified.
Usually there will be a noise, and its better to replace it (if its that bad only) with new one to prevent large amount of leak.
Looking at the gas mileage, I think its better to buy GT..But still not sure between it and Camaro.