first trip with 2022 chevy duramax 3500 flatbed . other than problem with filling tank , awesome trip. 1700 miles from alabama to arkansas 9.9 mpg average with cruise set 0n 65mph
OP said "FLATBED" right there empty wieght is typically 500-1000 lbs extra tare wieght over a pickup, depending upon what OP speed. Plus wind aerodynamics went down the road depending upon head board, goes it have an over the roof cab guard, or place to put a permanent attach tarp? If first trip out, most of us know mpg will be on lower side for first 5-10k miles..... I am surprised it was not 13-15. BUT OP was doing 65mph. Headwind?