2021 GMC Sierra 1500 4WD Crew Cab 147 AT4 with the AT4 Value Package, Technology Package, Driver Alert Package II, AT4 CarbonPro Edition, AT4 Preferred Package, Driver Alert Package I, and Preferred Equipment Group 4SB pairs a Duramax 3L I-6 diesel direct injection, DOHC, variable valve control, intercooled turbo engine with a 10-speed automatic transmission. With 277 horsepower and a strong diesel character, this Sierra AT4 brings confident capability, premium tech, and everyday usability together in one hard-working crew cab. If you've been looking for a well-equipped diesel half-ton, now is a smart time to move before this one gets away.AT4 Value Package adds well-judged upgrades that make the truck feel more complete and deliver stronger everyday value.Technology Package brings a more confident view around the truck and helpful driver information that makes parking, hitching, and tight-space maneuvering easier.Driver Alert Package II supports calmer highway driving by helping you keep pace, maintain lane position, and stay aware of traffic ahead.AT4 CarbonPro Edition gives the Sierra a more durable, work-ready edge with construction designed to handle demanding use with less worry.AT4 Preferred Package focuses on convenience and comfort, giving daily drives a more upscale feel without losing the truck's practical side.Driver Alert Package I adds extra awareness in busy traffic and crowded parking areas, making lane changes and reversing feel less stressful.Preferred Equipment Group 4SB ties the truck's trailering and everyday utility together so workdays and weekend hauling run more smoothly.Smart device mirroring keeps your favorite phone functions accessible through the infotainment screen, helping you stay connected while keeping your attention on the road.Mobile hotspot lets passengers and devices stay online on the move, which is a big plus for travel days, job sites, and family road trips.Rear camera gives you a clearer look behind the truck, which helps when backing into a space or lining up with a trailer.Forward collision mitigation adds an extra layer of confidence by helping the truck react when traffic slows or a hazard appears ahead.Front pedestrian impact prevention is there to help monitor the road ahead and respond when a pedestrian might enter your path.Lane departure prevention helps correct unintentional drifting, giving you added peace of mind on long drives and commutes.Adaptive cruise control takes some of the fatigue out of highway travel by helping manage speed and following distance automatically.Head-up display keeps important driving information in view without pulling your eyes far from the road.Brake assist can boost stopping power in a sudden panic stop, adding reassurance when