SAN DIEGO. In the face of stepped-up competition in the lucrative full-size pickup market, General Motors yesterday introduced HD (Heavy Duty) versions of its all-new 2007 GMC Sierra and Chevrolet Silverado to the media here.

General Motors said the redesigned HD versions “incorporate brand-distinct exterior and interior designs that are greatly differentiated from the light-duty trucks” along with a choice of gas and diesel powertrains and numerous heavy-duty standard and optional features.

Michael Tulumello, GM’s vehicle line director- full size trucks, told FleetOwner that the trucks, based on the new GMT 900 platform, feature the quality and value necessary to hold the line against market share erosion in the full-size pickup arena.

Perhaps GM’s best defense for holding its share is a strong product offense. “You never ever take your eye off Toyota,” Tulumello said. “They are a force to reckon with. They’ve come to market with the all-new Tundra. I don’t think they hit the ball out of the park but they took a real step forward. I believe that we have as well-- and we’re going to hold our share on the strength of the [2007 Silverado and Sierra].

“Between 2000 and 2005, the full-size pickup market grew by 350,000 units a year,” Tulumello continued. “We took 41% to 42% of that growth. We anticipate continued modest growth in the heavy-duty pickup side.”

According to GM, over the past two years it actually increased market share to about 40% in the face of a redesigned Ford F-Series and a retiring GMT 800 truck platform.

GM announced that standard equipment on the ’07 Sierra/Silverado 2500HD (3/4-ton) and 3500HD (one-ton) models includes a new variant of GM’s Hydra-Matic automatic transmission. The new 6L90 six-speed electronically controlled automatic delivers improved fuel economy, performance and handling, according to GM.

The 6L90 transmission has a wide overall ratio spread of 6.04, compared to 3.31 in the previous 4L80 used in GM’s HD pickups. The OEM said this allows a “steep” 4.03 first gear, which provides an improved performance “launch feel.” And with two overdrive gears – fifth and sixth – engine rpm is reduced by approximately 19% at 60 mph, for a reduction of about 400 rpm. GM pointed out that a lower engine speed reduces engine wear, improves fuel economy and lowers engine noise during cruising. The 6L90 has the capability for Driver Shift Control (tap up/tap down), Tow/Haul Mode and Auto Grade braking.

Other key HD features include standard Gen IV 6.0L V-8 gas engine with variable valve timing rated for 353 hp and 373 lb.-ft. torque and optional Duramax 6.6L turbodiesel engine boasting 365 hp and 660 lb.-ft. torque; “robust” four-wheel disc brake system and new integrated trailer brake controller.

HD models provide “segment-best” ratings of 18,500 lbs combined weight (with 6.0L gas V-8 and conventional trailer maximum weight rating of 13,000 lbs. Production of these trucks is slated to begin during this year’s first quarter.

See Smooth Ride for FleetOwner’s driving impressions of the ’07 Sierra/Silverado.

To comment on this article, write to Terrence Nguyen at tnguyen@fleetowner.com.