Chuck and Carol Right. No changes in the Engine or Transmisson, but body and other things like frame are changing. Go to this website and you'll see the "Newer" trucks listed as 2008.
http://eogld.ecomm.gm.com/
As i'm told it was a model change shut down by the truck plants to produce the much newer model with all the changes. GM would not let Dealers take new orders till Feb 8 2007 with delivery being about 6 weeks.
Then again, throw cash on the table and see how fast the salesman will either order or find you a newer one.