What's not easy about these behemoth vehicles is stomaching their fuel bills, oft the major criticism against the full-size SUV segment.

The 2007 Tahoe's 5.3L Vortec V8 now pumps out 320-hp and 355 lb-ft of torque, while delivering better fuel economy than the V6 engine powering Ford's mid-size Explorer. (Photo: Rob Rothwell, Canadian Auto Press)

The Chevy truck reps at the Tahoe's launch made a point of emphasizing the improved fuel economy of their fourth generation small block V8, which continues to displace 5.3 litres (325 cu in); the modifications to this venerable mill are sufficient alone to fill an entire review. It now pumps out 320-horsepower and 355 foot-pounds of deliciously smooth torque, but are you ready for this: it delivers better fuel economy in the big Tahoe than the V6 engine powering Ford's mid-size Explorer. And according to GM, it also out distances the V6 Kia Sorento with a litre of fuel.

U.S. EPA ratings give the 2007 Tahoe 2WD a fuel economy rating of 16 mpg city and 22 mpg highway (the equivalent of 14.7 and 10.7 L/100 km). The 4WD 2007 Tahoe is rated closely behind at 15 and 21 mpg respectively (the equivalent of 15.7 and 11.2 L/100 km). And as for the V6 Explorer, EPA assigns a rating of 15 and 21 mpg respectively (again, 15.7 and 11.2 L/100 km) for the 2WD version and 15 and 20 (15.7 and 11.8 L/100 km) in 4WD format. The Korean-built mid-size 2WD Sorento tips the scale

GM's Active Fuel Management (AFM) technology helps to beat smaller SUVs at the fuel economy game. (Photo: Rob Rothwell, Canadian Auto Press)

at 16 and 21 respectively while its 4WD edition dips the balance beam at 15 and 20 mpg (14.7 and 11.8 L/100 km).

So how did Chevy beat the mid-size V6-powered SUVs at the fuel-economy game? Well, lots of engine tweaking and re-engineering along with the application of GM's Active Fuel Management (AFM) technology, formerly labeled Displacement on Demand (DoD). Similar to DaimlerChrysler's Multi-Displacement System (MDS), AFM deactivates a series of valves, shutting-down four of the engine's eight cylinders when power demands are minimal. Is it detectable during driving? Not at all, and that's the beauty of this technology. When there's no need to run all eight taps, four automatically turn off. But it's unlikely the driver will ever notice, even when pulling the Tahoe's maximum tow rating of 3,492 kg (7,700 lbs) - well at least downhill.