I have a 2007 6.7 with 37,000 miles. I have done the California style deletes with the Smarty JRME. I have read on here from different people getting anywhere from 22 - 24 MPG with the Smarty and Deletes. I am only getting hand calculated 18 MPG and it says 20 on the overhead.
Is there something I have done wrong ??

 

No, most posters are reading the OHD and quoting this as their mileage improvement. I take most reported mileage gains with a grain of salt. Since there are many variables that effect the mileage on our trucks. Such as winter fuel, your driving style, what is the gearing in the truck, 4X4 or 4X2, SRW or DRW style truck and other factors.
What I base my improvements are on what I was and what I am now getting. If this has improved then that all that matters to me. I also track for a full year at a time an average this has my mileage improvement. I have three + years of data and have seen a steady improvement in my truck MPG gains from day one.
Jim

 

My overhead is reasonably close but my hand calculated, winter fuel, completely stock number was 14 MPG +/- 1.5 depending on how i drove it empty and towing was 10.5 on the only long distance towing run it had, after the california style deletes running an H&S mini maxx it went to 19 +/- 1 mpg depending on what im doing, unfortunately i havent had an opporotunity to do any real towing with it since the deletes but a friend needs a car hauled home from 2 hours down the road so that will be a good learning experiance and will report back tuesday or wednesday when i have some data to help your comparison haha

 

18 mpg is good, or at least not bad, if you using US gallons!
I did a 5" TB exhaust with a Smarty JR ME.
I went from 15 to 20 mpg, (in Imp. 19 to 25).
BUT...It dropped back to the original numbers when winter arrived.

 

17-20 HERE WITH 4.10s JUST DEPENDS ON CONDITIONS