General Motors' truck executives on Thursday showed off their highly refined, high-volume 2014-model 1500 series pickups, and re-emphasized product and image differences between Chevrolet's Silverado and GMC's Sierra.

The trucks, which go into production in spring and will be available at dealers shortly afterwards, will have a trio of efficient EcoTec3 engines; stronger, quieter, more comfortable cabs; electric power steering; stiffer frames; more supple suspensions; stronger brakes; and new lighting, tie-down and access features in cargo beds.

"The full-size truck market has shown renewed growth, fueled by pent-up demand following the recessional downturn," said Mark Reuss, president of GM North America, so the new series is well timed. He also noted there's been explosive growth in crew cabs for their work and personal-use versatility, and about six in 10 buyers now choose that four-door cab style.

Differentiation between the two brands continues the positioning of GMC as an upscale choice with the "professional grade" advertising theme, while Chevy ads will trumpet themes of tough truck and dependability, Reuss explained. Product differences are in grilles, headlamps, bumpers, and sheet metal contouring, and in interior-trim details.

Many features will be standard in GMCs and optional in Chevrolets, but details like LED front running lamps will be exclusive to GMC trucks. GMC noses have more chrome trim than those on Chevies, but an All Terrain model from GMC has a dechromed look to suggest off-road toughness. Both brands will continue to offer the Z71 off-road four-wheel-drive package.

The two brands share mechanical and electronic components, according to Jeff Luke, executive chief engineer for full-size pickups.

The EcoTech3 gasoline engine family includes a 4.3-liter V-6, and 5.3- and 6.2-liter V-8s, as now, but all get direct fuel injection for the first time. Variable valve timing and cylinder deactivation of current engines continue, as do advanced combustion and spark timing to control knock.

All three engines use lightweight aluminum blocks and heads and are mated with six-speed automatic transmissions. A cruise grade braking feature down-shifts the transmission on downgrades for reduced brake wear. V-8 models use new, larger 9.5- and 9.76-inch rear axles with the strength to accommodate the engines higher output.

The deactivation function turns the V-6 and the V-8s into four-cylinder engines to save fuel under light load, and reactivates the extra cylinders for more power when loads increase.

Horsepower and torque outputs are still to be determined by final testing, but are expected to be greater than from current engines. Actual numbers will be released later.

Sheet metal panels differ for Chevrolet and GMC versions, and great care was put into making them more aerodynamic, said truck styling chiefs from both divisions. This will reduce wind noise and improve fuel economy.

Mile-per-gallon numbers are also being determined, but GM will not promote those figures for the full-size trucks, said one executive. Revised mid-size Colorado and Canyon pickups, to be released in 2013, will be the company's truck economy leaders.

As of now, there will be no diesel offered in the new 1500s because the high cost of meeting exhaust emissions regulations raises diesel prices and makes them low value propositions.

The new pickups will offer two-door Regular, and four-door Extended and Crew cabs. The cabs carry over from current models, except that door tops are lower to improve aerodynamics, and the rear doors on Extended cabs are hinged in front to improve passenger access, execs said.

Nicer materials, more attractive styling and more comfortable seating are used for interior trim packages. Most get front bucket seats with multi-purpose consoles, with bucket-like contouring used in rear seats. Front bench seats will still be available in all three cab styles. Leather covers are used with higher trim levels while heated cloth seats will be available for the first time in GM pickups.

GM MyLink connectivity is via wireless Bluetooth and multiple USB ports. Natural voice recognition will allow hands-free controlling of electronic functions, including interfaced cell phone calling. An 8-inch color touch screen in the center of the dash comes with some "info-tainment" packages, and a 4.2-inch color screen information display is directly ahead of the driver in the instrument cluster.

Cabs are stronger, with nearly two-thirds of the structures made from high-strength steel for a confident feel and improved safety, executives said. Main rails and key crossmembers of the updated frames are high-strength steel with major elements hydro-formed for reduced mass and improved stoutness.

New shear-style body mounts tune out both up-and-down and side-to-side movement for a quieter, more comfortable ride. Extended and Crew cab models have a third set of hydraulic body mounts to further isolate the cabs from noise, vibration and harshness.

Cargo boxes are made from roll-formed steel panels that GM engineers say are stronger than competitors steel stampings. A new CornerStep bumper and handholds built into the top rail protectors ease climbing into the box. An EZ Lift-and-Lower tailgate is standard. Upper tie-down hooks and under-rail light-emitting diode lights are standard on GMCs and optional on Chevies.

Chassis updates for the 2014 full-size pickups include revised front and rear suspensions and wider wheels for a more comfortable ride and more confident handling. Electric power steering improves steering feel and reduces fuel consumption. New four-wheel-disc brakes have greater stopping power and Duralife rotors improve brake feel and last longer than previous designs.

Safety features such as Forward Collision Alert, Lane Departure Warning with an Active Safety Seat, and Front and Rear Park Assist are optional on Silverados and standard on Sierras. StabiliTrak with Trailer Sway Control and Hill Start Assist are standard on all models.

By the time they go into production, GM's new, full-size trucks will undergo more than 6 million miles of durability testing at company proving grounds in Michigan, Nevada and Ontario, executives said. Prototypes and pre-production trucks will accumulate more than 7 million highway and street miles during final testing, bringing total test miles to more than 13 million.

EcoTec3 engines underwent more than 10 million hours of computational analysis to optimize operating efficiency, they said. More than 6 million hours of analysis went into the advanced combustion system alone. Basics like new inlaid doors were tested to the equivalent of nearly 150 truck lives.

2014-model 1500 crew cab pickups will start production in the second quarter of 2013, with other cab styles following later in the year. Pricing will be announced closer to start of sale.