To be clear, there is a difference from the Job 1 and Job 2's as well as Generation 1 and Generation 2.
"Job" refers to the differences between the same truck. By that, the 01 had Job 1 and Job 2's as the body basically did not change but many things did.
Generation 1 refers to the 01 to the 05 (06 was not made) as there was a major body change done for the 07 model year...