I had a 2011 F250 diesel 4x4 CCSB before my current 2014 F350 4x4 CCSB. I saw 20 a couple of times empty, but mostly saw 16-17 and my overall average was 15.3 combined mostly highway occasional tow. My average towing was 11. My current avg with this one no towing is 13.
1996 Ford Bronco XLT OJ Special 5.8 3.55
2014 Ford F350 CCSB SRW Lariat 4x4 6.2 4.30
2011 Ford F250 CCSB Lariat 4x4 6.7 3.55 (sold)
1976 Ford Bronco Ranger 4x4 5.0 3.73 survivor (sold)
Several other Ford and non Ford vehicles both past and present