The gear ratio change should not have any impact on the speedo or the mpg "indicated" except that your mileage will go down because the engine is turning a higher rpm for the same speed. The speedo picks up at the wheel and doesn't care what gears are in it. Changing the setting with the Superchip, however, will affect the shift points. The tire size change is what changes the speed indicated and the mpg indicated. My actual calculated mpg from a verified distance and fuel used, went down with the larger tires and the gear change. Both were expected.
97 ZJ 5.2, Atlas, hp30, 8.8, alloys, locked F&R, Clayton LA lift, 35" KM2's
97 TJ 110" WB, Atlas, 350 chevy, D60, 14B, 42" Pit Bulls.