actually I think I read that it would be better for your transmission to have it tuned? But none the less having the ATX tuned will be a great improvement.
For what it costs for a tune I would do some more mods (intake, exhaust, etc) and then get a complete engine tune that includes the ATX (shift points, trans pressure, etc), make it worth your while.
If your serious about getting the tune talk to Tom or FSwerks.
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