26 mpg overall is excellent for a 4,500 suv. Consumer reports mixed driving yielded 18 for regular 3.5 L vs 24 for the Hybrid Highlander. A 6 mpg gain.
Now, I think careful hybrid drivers can always beat by a good margin folks who "just drive". That said, with 370 miles on the tank, I am at 28.8 since last refuel. We were 32 mpg the first 100 miles of mixed driving home from the dealer. Yet to actually fill up but plan on putting into the database. I would think a fully broken in hybrid would yield 1 mpg more.

I am an engineer and daily personal driver is a BMW 328 i 6m. I always get 30 mpg and with warmer temperatures 31 mpg looks easy as well. Consumer report says 24 mpg with auto. Depends much on the driver as well.