I get about 18mpg empty with my 2003 CTD. All stock 5.9. Edge tuner for gauges. I've only turned it up a couple times, but its an auto so I keep the program "economy" so the trans lives. About 245K miles on it. Did the injectors last year. Upgraded to the FASS pump/filtration to keep the new injectors happy. I'm one of those fools that likes daily driving at CTD for no good reason. I don't have anything new to add that has not already been said about maintenance.