When I first got mine, I was always hard on the throttle, & manually shifting the CVT. I was only getting about 23 MPG that way. If I leave it in "auto" & stay within the Eco range, I can get over 40 MPG with city driving & close to 500 miles on a full tank.
The air intake & exhaust do help to an extent. Tire size, compound, & pressure also make a huge difference with your gas mileage. Not to mention are cargo weight as well.