I'm stage 2 with a tp tune and I average around 20mpg.. Straight highway I will get anywhere between 25-28 mpg. But I drive like a old man most of the time. Most I have ever seen was 28.5 mpg and it didn't stay there.
The factory mpg gauge is not accurate. If you let your cat sit and warm up, your mpg gauge drops. I already calculate my mpg's at the pump.