Travel via the 2017 GMC Sierra 2500 full-size truck doesn’t include frequent fuel fill-ups. A week-long test drive of the 4WD Crew Cab Sierra 2500 showcased the mileage muscles of the new Duramax diesel engine. This driver saw highway mileage consistently hover at 18.9 mpg. That’s impressive fuel economy for a heavy-duty truck when it’s not hauling or towing. This engine gives the Sierra 2500 the highest diesel horsepower rating (445 hp at 2800 rpm) in its segment. The torque rating is 910 pounds-feet at 1600 rpm, a 19% increase from the 2016 model year Sierra 2500.

The 6.6-liter turbo diesel Duramax V8 engine mates to an Allison 1000 six-speed automatic transmission. (Base engine is a Vortec 6.0-liter V8 gasoline engine producing 360 horsepower at 5400 rpm and 380 pounds-feet of torque at 4200 rpm. The gas engine mates to a Hydra-Matic six-speed automatic transmission.) MSRP of the test-driven 4WD Crew Cab Sierra Denali 2500 powered by the turbo-diesel engine and fitted with an off-road suspension package, power sunroof and other options is $70,540. (Suggested base price of 2017 GMC Sierra 2500 is $35,085.)