I use premium in my N/A, and notice a difference, so I know the GT is gonna benefit a hell of a lot more from it. It's like using a different vescocity engine oil, you wouldn't do that would you? Like Sugamer said, 2 bucks a fill-up, is it that big of a deal? Definitely tell your dealer to use premium, and if you have to, cover the 2 dollars if they won't.
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