I'm in the market for a used truck too. Living in an emission testing area pretty much eliminated the 6.4 from consideration due to the inability to remove the DPF and EGR system. These systems choke the 6.4 in many ways, including that DPF regen that causes horrible fuel mileage and absurd levels of fuel dilution of the oil.
Call me crazy, but I'm looking at some 2006-2007 6.0 trucks. Once the trifecta of the coolant/EGR cooler/oil cooler is taken care of, these are pretty solid but that's a $3000 bill right there. The Cummins common rail engines are supposed to be good, but not the Dodge auto transmissions they are hooked too. 06-07 Duramax might be the best engine/transmission combo, but with a sticker price 10k more than a used 6.0. Seems with any of the big three diesels, you pay your money and take your chances.
