As with any modern Mustang, modifying a '13 Shelby GT500 starts with modifying to the programming inside the Copperhead PCM for more performance. Fortunately for Lethal, they have Jon Lund and Ken Bjonnes of Lund Racing (www.lundracing.com) on the case for tuning their cars and customer cars. Accordingly, the first mod was a custom tune (PN LP-JLCUSTOMTUNE-2013GT500; $200). It yielded gains of 34.55 hp and 15.27 lb-ft of torque without a single hardware change. Then the parts mods began.