I got as high as 23 under ideal circumstances on one roughly 300 mile trip. And I mean once. Typically my highway runs are in the 20 mpg range, which drops to maybe 16-17 on freeway runs averaging 82 mph. But I got as low as 13 freeway on a -10 degree New Years holiday run two winters ago. My city/suburb cycle nets me 16-17 on average.
Towing is consistently 10-12 with a 10k(+) fifth wheel depending on speed, terrain and conditions.
Lifetime EVIC shows 14.2 last time I checked. Overall I can't complain about my fuel economy given how much the truck weighs, how much towing I've done and how capable the thing is. A heavy duty gas truck would be substantially lower with my usage.