Gas mileage.... Is this normal?

[04SS99Denali]

winter i usually see a 1 mpg decreas. last winter my DIC said i was getting 12.9. between the winter fuel and the warming up in the morning mpg gets bombed.

 

[JochenWoern]

Calculate by hand for sure. Sometimes the DIC is pretty close but others I have had it as much as 1.7 mpg off of what I was truly getting. Today, for example, the DIC said 19.5 and by hand I was getting 18.3.

So, today I did calculate my mpg the "old fashion way/by hand".

My DIC called for 14.1 mpg, I calculated 13.5 mpg.

I guess the DIC is not too far off with 0.6 mpg and I could have topped it off a bit morte then last time as well.

 

[M3PO]

I have calculated my what my DIC says any times, and it has been very accurate.
I am sure if your speedometer is correct your MPG's would be fairly close. Now, if you have changed your gears and/or wheels, you might be showing a difference.