Onyx Black 2026 GMC Sierra 2500HD SLT 4WD 10-Speed Automatic Duramax 6.6L V8 Turbodiesel 10-Speed Automatic, 4WD, Black Leather. GMC Dealership Serving Boulder, CO Drivers Mike Maroone GMC GMC Sales, Service, and Parts in Boulder, CO If you have been longing to get into a new GMC close to Boulder, CO, then right now is an ideal opportunity to find your next auto at a low cost, here at Mike Maroone GMC. Enjoy Free Delivery anywhere in Colorado. Our GMC Truck line is headed by the Sierra 1500, 2500 and 3500, each new GMC model can be found here at our Boulder, CO dealership. Discover your new GMC in Boulder now for a test spin of your dream car. Recent Arrival! Price includes: $1000 - Buick & GMC Consumer Cash Program. Exp. 06/01/2026