From a few days ago. If you recall, I was distressed at having my mileage drop from 28-ish in mixed driving to 23-ish over the past 6 weeks. That's about a 20% drop.

I drove from Idaho to L.A. over the past 2 days.

Checked the odometer against the mile markers. It spins a little slow. I marked 98.4 and 98.6 on the odometer (both main odometer and trip meter) against two separate 100 mile highway stints. About 1.5% too low...but not enough to cause the issue.

Filled up in Oregon, Nevada (twice). Both times at between 20-35 degrees F and 4000-5000 feet elevation. Tank mileage was 23, 24 and 23.

Filled up at the bottom of the drop from Reno to Tracy. That was 44 (!) but it was a downhill run and only about 2 gallons. I discarded that.

Then on two fillups to L.A. I got 27 and 26, respectively. So it climbed up again once I got to warmer weather and lower elevation. Although it was clocking 28-ish during the summer in Idaho, where I'm at 2800 feet or so.

So somethin's goin on. Different diesel grades for different weather? Elevation and temp? All of the above?