Over at the Edmunds.com in the Highlander forum, I'm seeing reports such as:
Consumer Reports' reported 25mpg highway/12-13 city
One poster reports 21-23 highway @70-75mph
Another reports 23 highway/16-17 city

With 50/50 driving, that averages to:
Consumer Reports 18.75 mpg
2nd poster 19.75 mpg

Rick