You don't say what your issue is, but you could check into this. ( SVTP site thread )
08-16-4 SHELBY GT500 - CLUTCH DRAG
Publication Date: July 28, 2008
FORD: 2007-2009 Mustang
Some 2007-2009 Mustang Shelby GT500 vehicles may exhibit the following clutch/transmission symptoms: hard to disengage or engage 1st and reverse, hard to shift any gear, gear grinding during shifts any gear, vehicle creeps with trans in gear and clutch pedal fully depressed without brake pedal application, clutch slippage in gear with clutch pedal released, hiss noise with clutch pedal fully depressed (hiss on clutch pedal release is normal for GT500 clutch material). These symptoms may be due to flywheel distortion caused by excessive heat build-up during unique traffic conditions (example: severe stop/go urban driving). The distortion of the flywheel may prevent complete disengagement of the clutch. The system is designed for performance driving conditions.
Follow the Service Procedure steps to correct the condition.
NOTE: THIS ARTICLE APPLIES TO VEHICLES WITH PRIOR REPAIRS, AS WELL AS THOSE WITH MINOR MODIFICATIONS, EXHIBITING ABOVE SYMPTOMS.
NOTE: THE GT500 CLUTCH SHOULD BE DIAGNOSED/REMOVED/REPLACED AS A COMPLETE ASSEMBLY ONLY. DO NOT TAKE CLUTCH ASSEMBLY APART.
" Chance favors the prepared mind
2011 - lightly modded to 776rwhp
2014 - detuned to 780rwhp