I've got almost 20,000 miles on my '21 non-sas OBX 2 dr. 2.7. I have the 4.27 gears, and original tires/wheels.
I average 15/16 MPG. If it's all highway, I'll get 20. Pretty normal.
Here's a blurry vid of the tach. It's paired with a cheap Amazon Bluetooth dongle in the OBDII port. The app will run many more systems. You have to set up screens the way you want them.