Things are different everywhere. I know that.

Our '05 5.9 on-board mpg calculator is very close to gals vs mis. driven calcultions. Certainly within 1 mpg.

2 yrs in a row we've tried a "72 hour" chip. Both times less mpg.

Don't the 6.7 engines have more hp than the 5.9? Shouldn't that account for slightly higher fuel burn?