2027 Silverado 3.0 Duramax Fuel Economy Drops Again — An 8-Year Look at the MPG Decline

The 2027 Chevrolet Silverado 1500 equipped with the 3.0L Duramax diesel is receiving lower fuel economy ratings than the outgoing model.

The latest figures continue a downward trend that began several years ago, with the Silverado Duramax now rated considerably lower than when the engine was first introduced in 2020.

The original 2020 Silverado 1500 with the 3.0L Duramax LM2 earned an EPA rating of 33 mpg highway in 2WD configuration. For 2027, the updated LZ0 Duramax is rated at 27 mpg highway.

That's a reduction of 6 mpg, or approximately 18%, over eight model years.

The four-wheel-drive models have experienced a similar decline, and the latest ratings raise questions about how much of that reduction can be attributed to the engine versus changes to the truck itself.

2027 Silverado 3.0 Duramax Fuel Economy Ratings

GM-supplied fuel economy figures for the 2027 Silverado show reductions across the diesel lineup.

The standard 4WD configuration experiences the largest highway decrease, falling from 26 to 23 mpg.

The ZR2 loses just one highway mpg and maintains its 21-mpg combined rating.

The 2027 figures have been reported from information supplied by General Motors.

Chevrolet's original 2027 announcement also identifies the 27-mpg 2WD highway figure as a GM estimate. Complete 2027 Silverado results have not yet been independently confirmed in EPA's public fuel economy database.

Silverado 3.0 Duramax Fuel Economy History: 2020–2027

The Duramax has been available in the Silverado 1500 since the 2020 model year. Chevrolet introduced the original LM2 engine with 277 horsepower and 460 lb-ft of torque before replacing it with the updated LZ0, producing 305 horsepower and 495 lb-ft, for 2023.

Here's how the fuel economy ratings have changed.

Silverado 1500 Duramax 2WD MPG History

The 2WD Silverado provides the clearest illustration of the fuel economy trend.

The first two model years carried identical 23-city, 33-highway and 27-combined ratings.

Highway mileage decreased to 31 mpg in 2022, followed by another reduction to 29 mpg when the LZ0 arrived in 2023.

That 29-mpg rating continued through 2025 before dropping to 28 mpg for 2026 and now 27 mpg for 2027.

Silverado 1500 Duramax 4WD MPG History

These tables use the highest-rated standard Silverado diesel configuration for each drivetrain and model year, excluding dedicated mud-terrain and ZR2 variants. Some years have multiple EPA listings based on equipment or driving modes. In particular, the standard 4WD listing without Sport/Off Road Mode is 22/25/23 for 2025 and 2026, while the higher-rated variant achieves 22/26/24. Figures through 2026 are EPA ratings; 2027 figures are GM-reported.

The 4WD Silverado started at 29 mpg highway in 2020 before dropping to 26 mpg for 2021.

Interestingly, it recovered slightly when the LZ0 arrived in 2023, increasing to 27 mpg highway.

That improvement was short-lived. The highest available standard 4WD highway rating declined to 26 mpg for 2025 and 2026 before dropping to 23 mpg in 2027.

Why Have the Duramax Fuel Economy Ratings Decreased?

GM has previously attributed changes in Silverado Duramax fuel economy ratings to the vehicles and equipment used during EPA testing.

One example occurred with the 2021 Silverado.

When its 4WD diesel rating decreased from 29 mpg highway in 2020 to 26 mpg in 2021, GM explained to GM Authority that the test vehicle had moved into a higher weight class.

GM attributed the change to a more heavily equipped truck being selected for testing based on its production schedule.

For the 2027 Silverado, GM has again pointed to changes in vehicle configurations and equipment when discussing the lower fuel economy ratings.

However, that explanation doesn't necessarily account for the entire decline since 2020.

The Silverado itself has changed considerably over those eight model years, as has the Duramax engine.

When the LZ0 replaced the LM2 for 2023, GM revised the combustion system, fuel injection system, turbocharger and other components while increasing horsepower and torque.

The 2027 LZ0 receives additional hardware changes, includig revised pistons, piston rings, turbocharger vanes and emissions-related components.

The new Silverado also receives a redesigned body, revised chassis and different available equipment packages.

None of these changes can be individually identified as the cause of the fuel economy reduction without additional testing or engineering data.

Is the Duramax Actually Becoming Less Efficient?

There is an important distinction between declining EPA fuel economy ratings and declining engine efficiency.

EPA ratings measure the complete vehicle under standardized testing conditions.

The figures are affected by more than the engine itself, including vehicle weight, tires, aerodynamics, drivetrain configuration and calibration.

The 2020 Silverado Duramax and the 2027 Silverado Duramax are not identical vehicles. As a result, the difference in their published ratings cannot be used to calculate a corresponding reduction in engine efficiency.

However, buyers looking at a 2027 Silverado will see a lower fuel economy rating than buyers did when the original Duramax was introduced.

The 2027 2WD Silverado is rated at 24 mpg combined, compared with 27 mpg combined for the original 2020 truck.

Likewise, the highest-rated standard 4WD configuration falls from 25 mpg combined to 22 mpg.

Both represent a reduction of 3 mpg in combined fuel economy.

The 2027 Duramax Gets a Larger Fuel Tank

Although fuel economy is lower, Chevrolet has made a substantial improvement to available driving range.

The 2027 Silverado Duramax offers an approximately 34-gallon extended-range fuel tank.

Combined with the GM-estimated 27-mpg highway rating, that provides a theoretical highway driving range of 918 miles.

GM is advertising more than 900 miles of available highway range for the new Duramax.

For comparison, the 2026 Silverado Duramax 2WD uses a 22-gallon tank. At its 28-mpg highway rating, the theoretical driving range is 616 miles.

The larger tank provides substantially more available range despite the reduction in highway fuel economy.

Of course, driving range and fuel efficiency are two different measurements. The larger tank means fewer fuel stops, but it doesn't change the number of miles traveled per gallon.

Eight Years of Duramax Fuel Economy

The 3.0L Duramax remains one of the more fuel-efficient powertrain choices available in a full-size pickup.

However, its published highway fuel economy has steadily moved away from the figures that helped make the original LM2 popular.

The 2020 Silverado achieved 33 mpg highway in 2WD configuration. The updated LZ0 entered the market with a 29-mpg highway rating in 2023, followed by 28 mpg for 2026 and 27 mpg for 2027.

Four-wheel-drive models have followed a similar overall pattern, although their ratings have fluctuated more between model years.

GM's previous explanations demonstrate that testing configurations and vehicle equipment can influence these ratings considerably.

Whether the 2027 Silverado actually consumes more fuel than an earlier LZ0 under identical driving conditions remains to be seen.

For now, the published figures show an unmistakable downward trend in rated fuel economy over the Silverado Duramax's eight-year history.

Sources: U.S. Environmental Protection Agency Fuel Economy Guides (2020–2026); General Motors' 2027 Silverado announcement;