6.7 mpg's

[Rich3756]

My father in-law has a 6.7 that was released with the old mapping (purchased in Oct-Nov 2010) and when he had it serviced for the first time Ford remapped it with the new engine programming and he lost some mpg's, roughly 2-3. I am not familiar with the 6.7 fuel economy other than being better than my 6.4. haha So I was curious how significant the fuel economy gain would be by doing a tuner, exaust and CAT/DPF Delete. Thanks guys.