2020 Chevrolet Silverado diesel is the most fuel efficient pickup in America

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A new diesel version of Chevrolet's Silverado is giving the General Motors brand bragging rights for best highway mileage of any full-size pickup.

GM says the rear-wheel-drive diesel will get 33 miles per gallon on the freeway and 23 in the city.

That beats the diesel Ford F-150 by three mpg on the highway and one mpg in the city. An older version of Fiat Chrysler's Ram gets 27 on the highway and 20 in the city.

Even if you went four-wheel-drive, it's still going to be 29 mpg highway and 23 mpg city

All the figures are estimates based on Environmental Protection Agency tests.

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Silverado Executive Chief Engineer Tim Herrick says a new 3-liter inline six-cylinder diesel engine was designed for efficiency.

The Silverado's numbers are also higher than midsize Chevy Colorado diesel's, which has the same highway ratings as the F-150. The automaker says the Silverado benefits from the engine's advanced thermal management system, the use of a 10-speed automatic transmission and aerodynamic improvements.

The lead could be short-lived. A new diesel Ram is coming but mileage hasn't been announced. Both new diesels reach showrooms in the fall. 

The all-new motor puts out 277 horsepower and 460 lb-ft of torque. Those figures are higher than the Ford 3.0-liter V6's 250 hp and 440 lb-ft, but the aluminum-bodied F-150 offers the engine in models that can tow up to 11,400 pounds, while the Silverado maxes out at 9,300 pounds.

Chevrolet is making the diesel available in the Silverado's LT, RST, LTZ and High Country trims. It's a $2,495 premium over the 5.3-liter V8 in the LTZ and High Country, exactly the same price as the 6.2-liter V8 option. With the LT and RST, it's a $3,890 step up from the 2.7-liter turbocharged 4-cylinder, which is the Silverado's most efficient gasoline-powered engine at 23 mpg highway.

Chevy truck marketing boss Sandor Piszar expects the diesel to appeal mostly to retail buyers and make up less than 10 percent of Silverado sales, but said that the company is prepared to build more if demand warrants.

Information from FOX News and the Associated Press was used in this report.