I have driven many, many 5.9s and 6.7s. Drive a 6.7 with the auto, and you will see that it has more than the 5.9

 

How much improvment in power do you think you'd see if you did a DPF delete? I'd imagine that kills quite a bit.

 

The 2nd gens are still my favorite. I've been thinking about buying a few of them and warehousing them for future trucks and projects, Reading all of this makes me think I better get some 2nd gen 5.9s while there are still a few around that don't have 300k+ miles on them.