The GMC Sierra 6.6 Duramax 365hp (2008 - 2013) produces 365bhp and 894Nm in standard form. Our Stage 1 ECU tuning file raises output to 395bhp and 945Nm, a gain of 30bhp and 51Nm, with no hardware modifications required. The file is delivered through the ByteFLASH portal and is ready to write to the vehicle.