3.4 Swap MPG?

So I have completed a 3.4 swap. 96 auto into a 91 manual. Swapped to a manual computer & no codes! Am getting 13-14 MPG in town. Has 31's & is geared low. It revs at 3,000 rpm at 60 mph. Kinda looking for increased fuel savings with this swap. Is a gear change required to get better milage?