Our club president had his 08 GT tuned at Brenspeed and had nothing but good things to say about them. If they aren't too far for you, you could contact them. He drove out from Grand Rapids MI, so it wasn't a short drive for him, but he said it was worth it.
I second the vote for Paul's High Performance. A couple people I know have had their mustangs tuned there and have nothing but good things to say. I'm much closer to Brenspeed but only ever hear people around here recommend going to Paul's.
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