Natural gas has been getting a lot of attention lately. When record cold temperatures gripped much of the country this winter, it made headlines for its sudden high price. But natural gas as a transportation fuel continues to be significantly cheaper than gasoline on average, with the U.S. now producing so much of it that port terminals once used to import liquefied natural gas are being converted to liquefy and export it to energy-hungry markets like China and others. So when the 2014 Chevrolet Silverado HD offered a CNG bi-fuel option, it was only logical to assume it would be offered on the new 2015 body style.

The big changes to the 2015 HD CNG models are to the body and interior. This means much-improved interior design and materials, and a new double cab model replacing last year's extended cab, adding conventional front-hinged rear doors rather than last year's clamshell rear "suicide" doors. 2015 HD models also get integrated cruise control and Auto Grade Braking to improve driver control while towing.

The bi-fuel CNG option is available on all bed, cab, and wheelbase configurations of the 2500 model and on single-rear-wheel 3500 models. When equipped with the available 4.10 axle ratio, the Silverado HD can tow 13,000 running on either CNG or gasoline. Maximum payload ratings go down slightly when running on CNG. The engine on the 2015 HDs with the bi-fuel option is the familiar LC8 Vortec 6000 V-8. The engine produces 360 hp and 380 lb-ft when running on gasoline and 301 hp and 333 lb-ft when running on CNG. The package price for the bi-fuel trucks is $11,000. That's not an insubstantial premium, even compared with the $8395 for the Duramax diesel and mandatory Allison transmission, but fuel savings could be more than $2000 a year, so the cost could conceivably be recouped in less than six years.