2018 3500 120k miles.

These are typical performance mods that most of us here have.

Stage 2 trans from Inglewood transmission 35’s & 3:42 gears

The air filter isn’t dirty; the fuel filters changed, and there was no remedy.

I have been using fuel as if it’s a gas truck driving to and from work over the last week or so.

Would valve lash bring out of tolerance cause a drop in fuel economy?

Have exhausted all simple fixes that usually lead to a decline in MPG.