SCT Tuners for 2004 - 2005 Chevy GMC 6.6L Duramax LLY. SCT unlocks greater vehicle performance through ECU calibration, so your vehicle is better equipped to meet your specific needs. We've released performance calibrations for hundreds of vehicle makes and models from Ford, GM and Dodge. Our calibrations are quickly and easily uploaded to the vehicles engine control module using our handheld programmer technology. By optimizing vehicle calibrations, SCT tuning unlocks greater vehicle horsepower, torque and drivability. SCT aims to provide top-shelf performance when and where its needed most, and to continue as the benchmark for aftermarket tuning solutions.