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I was thinking about the exhaust and the only thing i can think of is if your driving more conservatively than it is more liable to produce carbon build up and that is burning off causing the sooty exhaust. the dealer can look at the fuel trim and injector flow to make sure everything is in spec.
TSB 9-23-8 I don't know if you had this concern or if it applies directly to your SHO but your dealer can tell you your latest cailbration and update if needed.
Some 2010 Taurus, MKS, MKT and Flex equipped with Gasoline Turbocharged Direct Injection (GTDI) engines and built on or before 10/14/2009 may exhibit diagnostic trouble code (DTC) P0096 intake air temperature: (IAT) sensor 2 circuit/range performance on bank 1. This may occur when the engine is at operating temperature and the vehicle is shut off and then restarted within five seconds. ACTION Reprogram the powertrain control module (PCM) to the latest calibration using IDS release 63.12 and higher or 64.01 and higher. This new calibration is not included in the VCM 2009.9 DVD. Calibration files may also be obtained at www.motorcraft.com.