The cheapest way to do it is get a Dallas Mustang's Speed Calibrator. Its about $100 and you can change the gear ratio to and from whatever you want.
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2004 Mustang GT 5 Speed
Mac O/R H Pipe
Mac Flowpath Catback
JLT Ram Air Intake
SCT XCal 2 Tuner
FRPP 4.10 Gears
13.191 @ 103.78
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