not sure about your mileage, using 91 to 93 octane will increase your MPG by at least 2MPG
My avg local/highway is 23.6 when I only do city driving I have been as low as 20-21mpg
I find the highway can be 26-30 depending on speed. My pump change there was a notice in mpg but may take awhile for the computer to average out new driving habbits