Wondering if anyone has had the same issue. I bought my 2012 2500 6.7 in July of 2015 and it had around 83,000 miles on it. Since I've had it, my mpg's both hand calculated and lie-o-meter have been anywhere from 10-13. 13 almost never happens but only in the summer on interstate trips. I was wondering if either valve lash, grid heater or CCV filter could be causing this? My grid heater is caked in soot but not to where air cannot pass through (thanks to the egr), intake horn was cleaned out thoroughly 5,000 miles ago, truck is emissions deleted and taken care of meticulously such as oil changes, fuel filter changes, and air filter changes. I figured if it was the grid heater being clogged, I would see more soot out the tail pipe from the inability to meet the desired AFR. For valve lash, I know that it is set differently from the factory for a stock exhaust system but would changing it make a difference? I do have 35's on the truck but even on stock tires, I was seeing the same mpg's. And as for the CCV I don't have any check engine lights or service messages but I don't have any record of it being replaced, I might just delete it and see? Can anyone offer some help? Those were just my assumptions but if anyone has any other ideas let's hear em!

Update:
Just finished doing the CCV Delete and needless to say I wouldn't wish it upon my worst enemy. It wasn't hard to do but just took a lot of patience. Plus it makes a mess if you don't do it over the trash! Just a heads up

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