All our new trucks in the last 2 years have come with "DEF" (Diesel Exhaust Fluid) set-ups. The trucks still use a DPF system (Diesel Particulate Filter), these help trap all the soot and suck and when the filter reaches a certain level it goes into "regen". Now regen is basically a big after burner, the system will inject and ignite diesel into the soot and it heats up to 1500-2000* and then burns it off. The DEF is only added to help bring down the NoX's if I'm not mistaken.
Big extra cost to your fuel bill for the sake of the tree huggers. But now you get lower miles per gallon, so burn more fuel, and your adding more DEF to the system to keep running...seems like the EPA don't know what the heck they're doing.