Just thinking out loud here but I did a quick google search and really didn't find much info on this but do you think the Silverado/Sierra might ever come with the 2.8L Duramax? The Duramax puts out 200HP and 370lb/ft of torque and that would be more than sufficient to move the truck around,that's the more power and more torque than the base 4.3 of yesteryear.

I imagine you could see in the 30mpg hwy with such a setup and it could compete against the Ram Ecodiesel. Obviously this motor would be the fuel Economy motor for these trucks and I'm willing to bet whoever had the most fuel efficient truck on the market will sell quite a few of them.