General Motors has unveiled pre-production hybrid versions of its Chevrolet Tahoe and GMC Yukon models, according to Automotive World. The full-sized SUVs will go on sale in North America in late-2007, according to a report carried by the Detroit News. Larry Nitz, GM’s executive director of hybrid technology, said that though work on the gasoline-electric SUVs is still in the development phase, the vehicles will be ready by the fourth quarter. Mark Cieslak, chief engineer for the new models, is quoted by the Toronto Star as saying the hybrid versions can offer 25-percent better fuel economy than the conventional Tahoe and Yukon. The report noted that GM plans to offer North American buyers 12 different hybrid models in the next few years. Tim Grewe, GM’s chief engineer for rear-wheel-drive powertrain hybrids, says the Tahoe and Yukon will be able to run on electric motors mounted inside the transmission, the gasoline engine alone, or a combination. The electric motors can also be locked out of the drivetrain for times when the engine’s power is needed, such as towing up to 6,000 lbs., according to Automotive World. Grewe said that both hybrid models feature a valve shutoff system that allows the 6.0L V-8 engine to operate on half its cylinders to help conserve fuel while running at cruising speeds. The models also feature 300-volt battery packs stored under the floor of the second row seats. In slow driving, the Tahoe can reach 25 mph without starting the gasoline engine. The interiors of the Tahoe and Yukon closely resemble their gasoline versions, the report claims. GM has reduced the weight of the SUVs by more than 300 lbs. partly by constructing the bonnet and tailgate of each from aluminum. Both hybrid models feature a small gauge in the dash, which tells drivers if they are saving energy or losing it through heavy acceleration or heavy braking.