I think it all comes down to cost, really. Ive gotta believe a DPF is expensive as well as EGR coolers, valves, etc. Then you have to get them certified by the EPA and good luck there. Those guys have their heads stuffed so far, you wont get anywhere. Even if you did get through all of that, how much would it really help? I dont think anyone is willing to spend the money and time on it.