2015 GMC Sierra 2500HD Denali Summit White 4WD Duramax 6.6L V8 Turbodiesel Allison 1000 6-Speed Automatic Priced below KBB Fair Purchase Price! Allison 1000 6-Speed Automatic, 4WD, Jet Black Leather. Odometer is 54581 miles below market average! Awards: * 2015 KBB.com Brand Image Awards