The 2027 Silverado's New V8s Aren't Thirstier. One of Them Is

Chevrolet's next-generation Silverado 1500 loses 1 to 2 mpg across its V8 lineup, according to GM documents first posted by GM Authority and reported by Jalopnik on November 3. The EPA has not rated the 2027 truck yet, so these are GM's numbers, not federal labels.

Here's what the "worse mileage" headline misses: it lumps two very different engines together. The new 5.7-liter V8 is, in my view, a free upgrade at the pump over the 5.3 it replaces. The 6.6-liter is not. If you're shopping the bigger engine, the real cost is roughly $600 a year in premium fuel, and that's the number worth arguing about.

GM's own paperwork shows a 1–2 mpg slide

Per the figures Jalopnik published, the 2027 Silverado with the 5.7-liter V8 and rear-wheel drive is rated 16 mpg city, 19 highway and 17 combined, with four-wheel drive giving up another mpg on the highway and combined. The 6.6-liter, offered only with 4WD, comes in at 14/18/15 mpg, and the ZR2 with the same engine at 13/15/14. Most diesel versions are 1–2 mpg worse than in 2026. The 2.7-liter turbo four has not been rated. Jalopnik expects the same figures to carry over to the GMC Sierra.

The engines themselves are bigger and stronger. Chevrolet's launch release for the 2027 Silverado lists 402 hp and 428 lb-ft for the 5.7 and 481 hp and 501 lb-ft for the 6.6. Kelley Blue Book puts the outgoing 5.3 at 355 hp and the 6.2 at 420 hp.

Engine for engine, the 5.7 holds the line

The fair comparison is not "2027 versus 2026." It is each new engine against the one it replaces, using the EPA's own 2026 records on fueleconomy.gov. The base 2026 Silverado 5.3 2WD is rated 16/20/17 mpg. The 5.7 matches it in city and combined driving and gives up one mpg on the highway. With 4WD, the 2026 5.3 is rated 15/19/17; the 5.7 is one mpg better in town and one worse combined.

Put money on it. I'm using 15,000 miles a year and AAA's November 4 national averages: $4.12 for regular, $5.04 for premium.

For 47 more horsepower, the 5.7 costs a typical 2WD buyer nothing and a 4WD buyer a couple of hundred dollars a year. That isn't a fuel-economy scandal. On paper, it's GM getting more power out of a bigger engine at roughly the same thirst, and it runs on regular unleaded. With federal fuel-economy rules being rolled back in a way that locks V8s in, that's the kind of V8 buyers should want.

The 6.6 is where the bill lands

The 6.6 is a different story. Two mpg combined sounds small until you remember the 6.2 it replaces already burned premium, per its EPA listing. According to autoevolution, citing the 2027 owner's manual, the 6.6 calls for 91 octane or higher, with 87 allowed at reduced performance.

That gap compounds. Dropping from 17 to 15 mpg over 15,000 miles is about 118 extra gallons, and at premium prices that's close to $600 a year. Next to a 4WD 5.7 on regular, the 6.6 costs around $1,175 more a year to feed. Over a five-year loan, that is a set of good tires every year, or a meaningful slice of whatever GM ends up charging for the engine option, which it hasn't published.

To be clear, 481 hp and 501 lb-ft buy something real. If you tow a heavy boat or camper often, the 6.6 may well be the right engine. My point is narrower: the extra 61 hp over the 6.2 has a running cost, and buyers should see it as a line item, not a rounding error.

The case against my view

The strongest objection is that I'm cherry-picking the 2026 baseline. The EPA lists several 2026 Silverado 5.3 variants, and the "with Sport Mode" 2WD version is rated 16/21/18 mpg. Against that one, the 5.7 is one mpg worse combined and two worse on the highway, which is roughly what Jalopnik's comparison implies. Measured that way, the 5.7 slips too, and my "free upgrade" becomes about $200 a year.

The second objection is the diesel. If the 3.0-liter Duramax, which GM's release describes as its proven diesel, also loses 1–2 mpg, then something about the new truck itself costs efficiency: weight, tires, aerodynamics or test conditions. That would mean every engine pays a tax, not just the 6.6.

I take both seriously, and I think they actually support the engine-level reading. If the new truck costs about a mpg on its own, as the diesel suggests, then a 5.7 that lands level with or one mpg behind the 5.3 is doing slightly better than its predecessor, not worse. The 6.6 losing two mpg on top of the same truck penalty is the outlier. And even on the least flattering baseline, the 5.7's cost is a third of the 6.6's.

What would change my mind

First, the EPA labels. Chevrolet says the truck goes on sale at the end of this year, so the official ratings should appear on fueleconomy.gov around then. If the 6.6 comes in at 16 mpg combined, or the 5.7 drops to 15, my math flips.

Second, regular fuel. If GM publishes output figures for the 6.6 on 87 octane and they stay close to 481 hp, the engine becomes a different proposition. On regular, a 15-mpg 6.6 would cost about $4,124 a year over 15,000 miles, less than the $4,448 a 6.2 on premium costs today.

Third, owner data. If real-world logs through the first half of 2027 show the 5.7 trailing the 5.3 by more than the label gap, the lab parity I'm leaning on doesn't survive contact with the road.