DETROIT -- Torque and towing, payload and ponies: They've long been the weapons of choice in the pickup wars.

But now fuel economy is reshaping the battle lines of the pickup market, and diesel engines are being thrust to the fore.

Nissan last week said it will try to shed its laggard status in the full-sized pickup market by dropping a V-8 Cummins diesel engine into its light-duty Titan for the 2015 model year. The move follows Chrysler Group, which will brandish its first light-duty diesel in decades when its Ram 1500 rolls out by year end with a V-6 from Italy's VM Motori under the hood.

Next up: General Motors, which is readying plans to offer a diesel in the next-generation Chevrolet Colorado and GMC Canyon mid-sized pickups, three people familiar with GM's plans told Automotive News. The redesigned pickups are slated to get a version of GM's 2.5-liter or 2.8-liter, four-cylinder Duramax turbodiesels, which power the Colorado in overseas markets. The diesel option will be added to the U.S. lineup about a year after the fall 2014 launch of the redesigned trucks, the sources say.

The shift toward diesels in full-sized light-duty trucks -- or even smaller pickups, in GM's case -- is the latest example of how toughening fuel economy standards are scrambling the competitive strategies of pickup makers, which typically aped one another's moves with incremental upgrades.

Historically, they sought a competitive edge through ever more powerful V-8 engines, or through nifty features, such as the RamBox storage compartment. But radical departures in powertrain technology were rare.

Now, with the addition of the forthcoming diesels, mid-sized and light-duty truck buyers will have an array of powertrain choices, from four-cylinder and V-6 diesels to turbocharged V-6s and diesel V-8s, coupled with fuel-saving features such as eight-speed transmissions, stop-start systems and cylinder deactivation.

The fast pace of innovation in the once-predictable pickup market has competitors scrutinizing one another's moves more closely than ever. Many industry insiders assumed Ford's successful EcoBoost V-6, launched in 2011, would impel GM to do a boosted engine of its own. So far GM hasn't bitten.

Even before upping the ante by announcing its diesel intentions, Ram turned heads with the segment-leading 25 mpg highway rating on its naturally aspirated V-6. Success for GM's Colorado and Canyon could force Ford and Ram to reassess their decision to ditch the market for smaller trucks.