The second owner of my GN kept really good records. When he had this car it was completely stock except for a hypertech chip.
From 1991 to 2003 he drove 28,394 miles and averaged 17.2 MPG over 12 years. Not sure what his driving habits were but over 28,000+ miles gives enough data points to feel pretty confident about his MPG. (and yes I plugged all his hand written records into a spreadsheet lol)
My 87 TR was getting terrible mileage on the hwy, like 10 mpg. Replaced the fuel filter and mileage went back up. I just got 21 mpg on city/hwy combo (90 miles city and 90 miles hwy). I usually get 15 mpg city, so maybe city has increased a little. Car only has K&N and stretched intercooler. Stock cam, injectors, turbo, transmission, Full Throttle chip.