I took a 100 mile highway trip yesterday...filling up when leaving, and filling up when I got back.
Using the % that my speedo/meter is off cause of my 38" tires....and then using the GPS to get real miles driven...my dash meter was only .4mpg off..
It said 18.6, and I figured long hand 18.2
This is with the Spartan tuner on the 250+ tune.
Pretty damn good!