My stock white gtp gets about 17-18 city driving civilized and i don't know what it gets on the highway because I have yet to drive it on the highway.

My rusty blue gtp is rock solid at 19 mpg all city with me constantly beating on it (has a 3.5 and headers/needs retuned) and last time I had it on the highway (few years ago when I got rid of it) it would get 31 mpg all day long and 35 mpg without the hood