Another one bites the dust; this time General Motors has decided to place on indefinite hold its previously announced plan to add the highly anticipated, all-new Duramax 4.5-liter V8 diesel engine in 2010 to its Chevrolet Silverado and GMC Sierra light-duty trucks. "We remain optimistic that the Duramax 4.5L V-8 diesel may be a viable option in its future portfolio," said the company in a statement.For the time being -and who knows for how long- Chevrolet and GMC will continue to offer a Duramax 6.6-liter V-8 diesel in their heavy duty pickup trucks. Recently, GM launched 2-Mode hybrid versions of the Silverado and Sierra that received an EPA estimate of 21mpg in the city and 22mpg on the highway (2WD versions). With the new 4.5-liter V8 diesel, it was estimated that the trucks would have achieved a fuel economy in the high 20s mpg.