I was averaging between 10.8 and 11.4 in town with my 99 EB 5.4. I put a single Flowmaster on, complete tune up and K/N. I didnt notice any change. I since added 2" and 33,s. I then put the performance tune[Superchips 1715] and I run 89 octane.

I steadily saw the mpg rise and on a trip to Myrtle Beach,SC[roughly 260-ish miles] Combined hwy and two lane roads I averaged 15.7. Running between 55 and 75 with the a/c full blast.

While in MB, I averaged 14.2-14.6. I was blown away.Since I have been back, Im still in the lower 14 range.

I do the numbers on my own and watch the overhead.