Originally Posted by Matt_Nauman

General Motors' first full hybrid reaches showrooms in November, and now that I've driven one, I can testify that it arrives as promised. Sold as either a Chevrolet Tahoe Hybrid or a GMC Yukon Hybrid, it's a full-size sport-utility with as many as eight seats and the capability to tow a boat that also delivers a fuel-economy gain and can even run on pure electricity
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The 2008 2WD GMC Yukon with a 5.3-liter V-8 gets 14 mpg in the city and 20 mpg on the highway, according to the government's www.fueleconomy.gov Web site. Using Bly's numbers, that means the hybrid (which uses a 6.0-liter V-8 for better low-end torque) ought to get 19 to 20 mpg in the city and 21 or 22 mpg on the highway. The vehicle is undergoing certification right now, he says.
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The hybrid components, including the 300-volt nickel-metal hydride battery pack, add about 400 pounds to the truck's weight. Engineers took out 320 of that by making lighter seats, making the hood and rear hatch out of aluminum and removing some unneeded bits such as the starter motor and alternator.
Designers made the vehicle more aerodynamic, with a new front end, a rear spoiler and even new wheels and running boards that lessen wind resistance.
The battery pack is under the second seat, so passenger and cargo room remains the same.
The 2-mode hybrid transmission - "a piece of art," Bly says - fits into the same space as a standard six-speed automatic. It contains two 60-kilowatt motors, and has four fixed gears, three planetary gear sets and four clutches.
It, plus regenerative braking, allows improvements in both city and highway driving, thus the 2-mode designation. In the first mode, either electricity, the gas engine or both operate. In the second mode, at highway speeds, the electric bits boost the gasoline V-8.
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