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DALLAS – The first politically correct full-size SUV is about the hit the market – with a city fuel-economy rating the same as that of a four-cylinder Toyota Camry or Honda Accord.

It’s not a Toyota or Honda product, or even a Japanese vehicle at all. This breakthrough sport utility vehicle comes from General Motors Corp., and is built right here in Tarrant County.

Actually, it’s two vehicles that are almost identical: the 2008 Chevrolet Tahoe and GMC Yukon gasoline-electric hybrids.

Their EPA rating of 21 miles per gallon during city driving is a 50 percent improvement over the regular gasoline-only versions of these big SUVs.

It’s also in line with many midsize cars equipped with four-cylinder engines, including the Camry, Mazda 6, Hyundai Sonata, Volkswagen Passat, Chrysler Sebring and Dodge Avenger. It even beats some of the four-cylinder sedans, such as the Ford Fusion and Mercury Milan (20 mpg city).

And when compared with V-6 powered versions of popular family sedans, the V-8 and electric-motor powered Tahoe/Yukon has better city fuel economy. The V-6 Camry and Accord have 19 mpg city rating; the Fusion, Ford Taurus and Mazda 6 are rated at 18 mpg city.

All of these ratings have been compiled using the new 2008 EPA formula, which is designed to be more realistic than the government’s old way of estimating fuel economy. The highway mileage rating is 22 mpg for the two-wheel-drive. Four-wheel-drive models are rated at 20 mpg city and highway.

GM says overall fuel economy of the hybrids is about 30 percent better than that of comparable gasoline models.

The gasoline Tahoe and Yukon models are EPA rated at 14 city/20 highway for the two-wheel-drive versions with the 5.3-liter V-8 engine.

“The new Tahoe and Yukon hybrid SUVs offer the best of both worlds to customers and complement the Texan lifestyle – all the capability expected of an SUV with better-than-ever fuel economy,” Chevrolet General Manager Ed Peper said during the recent public introduction of the new hybrids at the State Fair of Texas, just a few miles from yjr Arlington plant where the vehicles are built.

The two hybrids are on public display at the fair through Oct. 21.

Prices have not been announced yet for the hybrid models, which will go on sale sometime before the end of the year, the automaker said.

Under the hood of these vehicles is a 6.0-liter V-8 engine equipped with GM’s Active Fuel Management system. It’s designed to cut out four of the cylinders during highway cruising.

During the Nashville test along Interstate 24, this system engaged on level ground and during slight downhill grades with the cruise control set at 70 mph. An indicator on the dash shows when the engine is in four-cylinder mode.

Any slight upward incline brought the engine back to eight cylinders. (This system also is used on gasoline-only Tahoe and Yukon models with the 5.3-liter V-8 engine, giving them an EPA highway rating of 20 mpg (two-wheel drive).

The cylinder cutout does not work at low speeds, but that’s where the electric motor works best to increase fuel economy, especially in stop-and-go city traffic.

Besides having the fuel-saving gasoline-electric setup, these so-called two-mode hybrids can run on solely electric power at low speeds, just like the groundbreaking Toyota Prius hybrid.

As with the Prius, the gasoline engine stops when the vehicle comes to a halt, such as at a red light.

The Tahoe/Yukon can start out using only the electric motor until about 30 mph, when the gasoline engine kicks in automatically. This would happen only with light pressure on the accelerator pedal, however. With inefficient jackrabbit starts, the gasoline engine comes on immediately.

During a test drive of the Tahoe hybrid recently in Nashville, Tenn., I found it difficult to drive for long on the electric motor, but I was able to do so with a just-creeping start.

The second mode of the Tahoe/Yukon hybrid system kicks in at passing speeds. Then, the electric motor comes on to give the vehicle a boost in power, helping to save fuel.

Electric power assists the engine during trailer towing as well, GM says. Fuel savings also occur during deceleration, when fuel is automatically shut off and the hybrid battery pack is recharged using so-called regenerative braking.

“Building the full-size SUV hybrid vehicles locally is a perfect fit for Texas,” Arlington Plant Manager Alicia Boler-Davis said.

“Most auto manufacturers offer hybrid vehicle technology only in smaller vehicles with less room for passengers and cargo. In Texas, we know transporting family and towing boats, campers and trailers is a way of life.”

The body and interior of the Tahoe and Yukon hybrids are the same as their gasoline-only counterparts, both of which were redesigned for 2007.

Changes for 2007 were quite comprehensive, making an already good product even better.

These vehicles were the first large SUVs to break the 20-mpg barrier for highway fuel economy, using the 5.3-liter engine and the cylinder shut-off system.

The Tahoe is the best-selling full-size sport utility; the GMC model doesn’t sell as well, but only because there aren’t as many GMC dealers as Chevrolet.

These are not wimpy vehicles like many of the other hybrids. They are built on the new GM 900 vehicle architecture that also is the basis for the redesigned Chevrolet Silverado and GMC Sierra full-size pickups.

Each has a fully boxed steel frame, a coil-over-shock front suspension, rack-and-pinion power steering, and a carlike interior.

While they are trucks underneath, they have the feel of premium cars.

The Tahoe and Yukon’s wide front and rear tracks “enhance handling and lower the center of gravity for a more-confident road feel,” GM says

All Tahoe and Yukon models come with GM’s 360-degree occupant-protection and crash-avoidance technologies, which include electronic stability control with rollover mitigation, as well as head-curtain side air bags for all three rows of seats.

The hybrid system used in these vehicles was co-developed by GM, the former DaimlerChrysler and BMW. It’s designed for use with either gasoline or diesel engines, although at least for now, GM is sticking with a gasoline engine at least for the North American market.

There are two electric motors with the GM system, both contained within the automatic transmission.

“A sophisticated controller determines when the vehicle should operate in either mode,” GM said.

“Input from the controller determines the necessary torque for the driving conditions and sends a corresponding command to the engine and electric motors.”

GM says that gears in the transmission “multiply torque similar to a conventional automatic transmission to propel the vehicle.”

But unlike conventional continuously variable transmissions, the Tahoe/Yukon’s system has no mechanical belts or bands, the automaker said. “Shifts between the two modes are synchronous, which means no engine speed changes are necessary for the mode shift to occur, resulting in ultra smooth accelerations.”

The electric motors and the rest of the vehicles’ electrically powered systems draw their power from a 300-volt nickel-metal-hydride battery pack under the floor. Converters are used to drop the voltage to run 12-volt systems such at lights, radio and air conditioning.

The battery pack is recharged while the vehicle is decelerating or whenever the gasoline engine is running, so the vehicle does not have to be plugged into an external AC power source.

One of the electric motors doubles as a generator, and also is used as a starter for the gasoline engine.