Chevy Tahoe Hybrid | It's fuel efficient! No, it's a gas guzzler! Yeah, well, it's both

The Chevy Tahoe Hybrid is as provocative and political a vehicle as you'll see this year. Why, it's practically a polemic.

By way of a fantastic exertion of technology and human capital — which I hereby honor and praise even as I question them as misallocated — GM has managed to give one of its behemoth SUVs marginally better fuel economy.

The two-wheel-drive hybrid Tahoe returns an EPA-estimated 21 miles per gallon in the city, 22 mpg highway; the 4x4 version rates an even 20/20, city/highway. The company and its various choristers — such as the Green Car Journal, which recently named the Tahoe Hybrid "Green Car of the Year" — are pleased to point out that represents up to a 50 percent improvement of in-city fuel economy over the non-hybrid Tahoe.

The objectors have rebelled against the symbolism of the thing. It might be half-again better, but it's still an awful, blot-out-the-sun SUV. Isn't this like putting handlebar tassles on the wingtips of a 767 jet?

I had a chance to spend a couple of days in the Tahoe Hybrid — white, with gold "Hybrid" decals. People have accused Prius owners of being ostentatiously green, but the badge-barnacled Tahoe might as well have roof-mounted green emergency lights and a "Green! Green!" whoop siren.

So, what's it like? For sheer execution, you can do nothing but throw rose petals at the thing. The engine starts instantly — as you would too if you were goosed with a 300-volt battery pack — and looks for opportunities to shut itself down, such as when the vehicle is coasting, braking or stopped.

If you feather the accelerator just right you can make the Tahoe Hybrid sluice along at up to 30 mph in all-electric mode. It has two honking 60 kW traction motors.

The system exploits the otherwise-lost kinetic energy of the drivetrain during coasting and braking, with the traction motors switching polarity to become generators, pumping up the traction battery.

GM calls it a "two-mode" system, though I'm not clear even now what the two modes are. I count three: electric only; gas only; and/or gas-electric, in which the operating system constantly ciphers the fuel-saving optimum.

Meanwhile, the Vortec V8 employs what GM calls active cylinder management — other companies call it cylinder deactivation — that chills out four cylinders when demand is light.

If you wanted to send a congratulatory case of beer to anybody at GM, address it to the software writers — whose ka-jillion lines of code keep the engine, transmission, batteries and motors in a constant state of reification.

Spare a six-pack for the transmission's designers, for it is the transmission — with its three planetary gearsets, two integrated motors (with their own reduction gears) and various other hardy fitments — that allows the Tahoe to tow 6,200 pounds, a tonnage that would fatally herniate a Toyota Highlander Hybrid.

Put the power down and the 5,700-pound SUV goes like a rear-ended boxcar: The combined output of engine and motors is a romping 332 hp and 367 pound-feet of torque, much of it at low rpms.

What's astonishing in even a cursory round-the-block test drive is the seamlessness, the absence of shudder or second-order vibrations, with which all this heavy-duty machinery goes about its business.

Behind the wheel, the Tahoe Hybrid has the cues of a regular Tahoe, including a cabin the size of a handball court. Here and there are signs of a light-weighting program undertaken to counteract the added hardware and batteries: The upholstery is thinner and lighter. The Hybrid makes use of loads of alloys, including lightweight wheels, aluminum hood and liftgate. And the Hybrid uses low-rolling-resistance tires.

So isn't this champagne-popping territory? Yes, no. ... Some inconvenient questions:

First, what would the mileage of this vehicle be with all the improved aerodynamics, low-rolling resistance tires and aluminum body panels, yet without the fretful weight (and cost) of the hybrid system? What is the cost-benefit ratio of the hybrid system apart from these improvements? And shouldn't the improvements be standard issue on all big SUVs?

It's hard to tell exactly what the "hybrid premium" is on the Tahoe Hybrid (MSRP of $50,490) but it looks to be, at a minimum, $8,000. That's a huge lump. One argument to celebrate this technology is that it could be mainstreamed into the hundreds of thousands of GM's trucks and SUVs.

But how realistic is that? Does this super-low-volume program do more for corporate image than corporate average fuel economy?

What is this program's budget? How does it compare to GM's ad budget for it? Isn't this just what critics call "greenwashing"?

Perhaps the problem with judging the Tahoe Hybrid harshly — it does seem absurd on the face of it — is that we don't know, or little appreciate, the larger plan at work. Perhaps GM means what it says when announcing that it plans to electrify personal transportation and has tackled the biggest challenge — its most fuel-thirsty products — first. Could it be we're being cynical about a good-faith effort?

What really needs to be re-engineered, of course, is the consumer, who needlessly opts for these big, heavy-duty vehicles (I assure you, people, you don't need a Tahoe to trailer your 300-pound dirt bikes). This is a contentious issue, since Americans feel they should be able to drive whatever they can afford, disregarding the fact that the sky — and our collective debt of foreign oil — is part of the public commons. Plenty of people regard any attempt to regulate the vehicle fleet as Kremlin-esque social engineering.

For now, we have this paradox, a fuel-efficient vehicle that's still a gas hog. A hybrid that's simultaneously good (promise) and bad (reality). Matters could only get more muddled if a hybrid Hummer comes rolling out.