htrod4d

Can anyone shed some light on the difference between the 02 -03 8.1 and the 04-07 8.1. I have what is titled as an 04 winnebago adventurer with the 8.1 and the motors junk. But you never know exactly when the chassis was built. could have been 03 or 04. When looking up engines every site shows a cut off from 03 to 04 and I don't know why. Any help would be great. And yes this is my first GM in a long time.