I just had mine replaced at a top notch diesel shop here in GA, I dropped 4-5 MPG after my first tank. I've got a call into the owner of the place to see what they have to say, I can't believe that the firmware update is the only thing that is causing this. I'll let you know what they say.

 

I wonder if the shop in Ga is the one I am thinking of ...................

I donlt doubt that it is probably the flash, but I recently had a brake caliper dragging and when fixed I picked up at least 1 mpg. I didn't realize it was dragging until it got real bad (smoking and stinking).

 

Another one here...Got a new replacement FICM from ford and haven't hand calculated yet but the lie-o-meter shows a drop of about 3-4mpg. The truck was down a long time (whole different story of USPS misplacing my original FICM back from PHP) so first run out the brakes were sticking and smoking. I think i got that taken care of though...