OK, I jumped the gun a little bit and didn't go the usual 340 miles or so. Filled up at 279.9 miles with 18.578 gallons which calculates out to 15.06 MPG.
What the heck is that all about? What is going on with this truck? I can't recall any appreciable difference in driving style or weather conditions.
Maybe somebody siphoned off a gallon or two while I was parked at the shopping center where I meet my carpool.