Alright, here it goes...
I have had one of each of these pickups, 6.0, 6.6, 5.9, 7.3 and a buddy with a new 6.4, and I will tell you this, the only one I would even look at for a purchase is a new 6.4. I am currently trying to get rid of a 2007 5.9 with every option and I can't stand it. It will rattle you do death, or the tranny will leave you in the dumps. Bottom line is that the 5.9 is great if they ever put it with a transmission or a pickup worth driving. The duramax is good if they ever put it with a pickup that would hold together for something other than a grocery getter. The Ford finally pulled a motor together that is up to snuff with the tranny they have developed and the pickup they have wrapped around it.
As one last comment to anger the remaining cummins folks, the stock tranny in my NEW pickup under STOCK conditions, has come apart twice!
This is 325hp at the crank! No 4spd tranny from Dodge will ever handle 600hp!