The revamped, full-size Chevrolet Tahoe and Suburban and their GMC Yukon/Yukon XL twins gain significant length, interior volume, and creature comforts for 2021, but extra MPGs seem to be in short supply.

The vehicles are now even larger than their predecessors, are still heavy, and carry identical V8 engine displacements, so no one should have expected Prius fighters. Still, the changes in fuel economy are worthy of note.

Still unlisted on the EPA's fuel economy site, the models had their MPG figures released by GM this week. What we can see is that, while efficiency sees a gain in the city, that improvement is offset by decreased thriftiness on the highway.

It breaks down like this: in 5.3-liter, RWD or 4WD, short-wheelbase guise, the 2021 GM full-sizers rate 16 mpg city, 20 mpg highway, and 18 mpg combined. The previous-generation 5.3L short-wheelbase models earned 15/22/18 in rear-drive guise, 15/21/17 with four-wheel motivation.

The lengthier 5.3L models match these figures in rear-drive form, but lose 1 MPG in each driving cycle when equipped with four-wheel drive. EPA ratings for the old-gen 5.3L long-wheelbase models stand at 15/22/18 (RWD) and 14/21/17 (4WD).

Inclusion of a standard 10-speed automatic and GM's Dynamic Fuel Management helped the V8 manage its thirst around town, but it seems all the new added hardware (tech niceties, independent rear suspension, size) causes the hulking SUVs to imbibe more heavily on the highway. Highways are for AAA, not AA, it seems.

Opt for the 6.2-liter in either the Tahoe or Suburban, and the EPA rating comes out to 16/20/18 regardless of the driveline type. No penalty here for going bigger (minus the cost, of course). The new models in 6.2L guise slightly top their predecessors in both city and combined economy.

It all sounds unimpressive until you consider GM's decision to offer the company's new 3.0-liter Duramax inline-six diesel in all such models (including the Cadillac Escalade). Boasting 277 horsepower and 460 lb-ft of torque, the Duramax variants' MPG rating remains unknown, but one look at the Chevy Silverado's ratings suggests significant improvements in efficiency for so-equipped models. Chris was pleased with what he saw in a recent test of a new Duramax-powered Silverado 1500.

a version of this article TTAC