Damn you guys got some heavy a$$ right feet!

I got some very heavy mods, weigh in at close to 7000 lbs, and get about 12.5 in town and close to 16 on trips with 35" tires!!!

 

If i'm driving in the city and reset the thing on top im averaging 10-12, but as soon as i hit a red light esp for a while, the digital thing on top shows only 8-9...how reliable is it?

 

Mine is usually off about 1-2 mpg when compared to reliable hand calculations. My overhead in the truck ALWAYS shows better than what I'm getting and my speedo is calibrated to within 1/4" of my actual measured tire height.

Interestingly, the overhead in my Jeep Grand Cherokee is always within 1/4 mpg of my hand calculations.

The reason you are showing worse when sitting still is that you are burning gas and NOT going anywhere, even though you use relatively little gas idling, the 0 mph is gonna kill gas mileage...