While the 2020 GMC Sierra 1500 may not be as fuel-efficient as an electric truck like the Tesla Cybertruck, but its fuel economy may shock you. For a traditional, full-size pickup truck, the best way to get a great fuel economy is by equipping it with a diesel engine. And when the Sierra was tested with its diesel engine, its fuel economy was better than expected.

What the EPA says about the 2020 GMC Sierra 1500

When the government tested the Sierra with its 3.0-liter V6 diesel engine, the EPA got a fuel economy of about 23 MPG in the city, 30 MPG on the highway, and 26 MPG combined. That said, those figures are for the Sierra in its two-wheel drive configuration, which isn’t a popular option for truck lovers. 

The four-wheel drive option for the Sierra, when it’s equipped with that same V6 diesel engine, got a slightly worse fuel economy. The EPA said that it got 22 MPG in the city, 26 MPG on the highway, and 24 MPG combined. Overall, those are minor losses in fuel efficiency, but since four-wheel drive is such a popular and necessary option, this is the more realistic fuel economy of the Sierra. 

What the tests actually showed

When people actually got their hands on these diesel trucks, the results were a bit different than what the EPA got. For Ram, despite the fact that the Ram 1500’s diesel engine is more powerful and supposedly as fuel-efficient as its competitors, news outlets actually reported a worse fuel economy than expected. In the Ram 1500’s case, it was to the tune of about a 4 MPG difference. 

On the other hand, while the V6 diesel engine on the Sierra and its cousin, the Silverado, is less powerful than the diesel on the Ram 1500, these diesel engines, when tested by news outlets like Pickup Trucks, actually showed a higher fuel economy than what the EPA said it’d do. 

In the Silverado’s case, PickupTrucks.com and other journalists were posting fuel economies of between 34 MPG to 45 MPG, and both of those numbers are significantly higher than what the EPA said that the Silverado could do. In the Sierra’s case, PickupTrucks.com explains that the Sierra does have a less aerodynamic design than the Silverado does, so it should get a slightly worse fuel economy despite having the same diesel engine. 

PickupTrucks.com, when it tested a two-wheel drive Sierra with that V6 diesel engine in a 200 mile run through both cities and highways, reported a combined fuel economy of about 32 MPG. The reviewer says that its tested fuel economy was 6 MPG higher than what the EPA says it’d do. 

What this could mean for the 2020 GMC Sierra 1500

A lot of things other than an engine and the design of a truck can affect its fuel economy, so it’s possible that this was just a fluke. That said, a 6 MPG difference, even in a two-wheel drive Sierra, is still extremely significant. That’s a 23% improvement over what the EPA said that the Sierra ought to do. 

Furthermore, the onboard computer of the Sierra, according to Pickup Trucks, reported an average fuel economy of about 30.6 MPG. This is less than what reviewers calculated, but it’s still better than what the EPA got from its tests. 

Additionally, because the Ram 1500’s diesel engine did do worse than expected in its real-world fuel economy tests, the Sierra and the Silverado gets a leg up on the Ram 1500. This is important, as these trucks, along with the Ford F-150, are four of the most popular trucks in America. Any differences between them can be the difference between buying a truck or not buying a truck.