"Have you had any emissions issues with the Cummins?"
Not really. The only problem I have had with it is a clogged egr tube. It threw a code and slightly de-rated. My truck is a 2010, (I got it new fall 2009) so no def, just regen. I run the truck very hard going back and forth over Donner Summit. It gets good and hot for mile after mile. About the only time it regens is when I run the pto for long amounts of time.