In the last 4 years I've had (long story): SR5 premium, 2018 Limited, 2019 TRD Pro, and now a 2020 Limited and never got above 18 or below 15.

15-17 is a reliably good number for typical fuel economy for these rigs.

I briefly had a Highlander that got 25 mpg in same driving conditions.

You can expect a 2-4 mpg drop in real world conditions.

I live in W. Texas as well. The issues are lots and lots of headwinds all year around and de-facto 80 mph speed limits literally everywhere. Throw in tire pressures set for optimal wear and ride comfort, and you are gonna move the needle.

Only way I got window sticker MPG was to drive with the wind and go 70 mph or lower.