My last truck was a 2008 6.7 4x4 that I bought new. It was a pretty good truck while I had it, but I deleted all the emissions stuff within the first few weeks. I realize that's not an option for everyone, but the older EGR/DPF trucks were pretty problematic for most. The only thing I had go wrong was the water pump, which is apparently a common Cummins failure. The newer (2012+?) trucks use DEF, I not sure if they're as trouble prone or not?

I ended up getting rid of it after I realized a diesel wasn't right for me.