I didnt realize Chevy made a 7.8L I6 for their bigger trucks! Looks suprisingly just like a Cummins block to me yet it only makes 200HP.

http://www.shadetreemechanic.com/duramax_diesel.htm
Scroll 1/3rd down the page.

Edit: Sorry, I didn't realize Isuzu made it...

 

Seems like a real slug. But probably a stout long lasting engine. Could easily see 200k!
That first picture... Is that the new '07 Silverado? Looks better! I like the retro look!