CARFAX One-Owner. Clean CARFAX. Onyx Black 2017 GMC Sierra 2500HD SLT 4WD Allison 1000 6-Speed Automatic Duramax 6.6L V8 Turbodiesel Fully Detailed, Allison 1000 6-Speed Automatic, 4WD, jet black Leather. Awards: * 2017 KBB.com Brand Image Awards