I have a 98 blazer with a 2'' lift and 31" tires. Since the tires are bigger, that means the odometer is going to read off? How much will it read off from stock. Secondly i have a mildly heavy foot, and have posted 230 miles off of 15 gallons(before compensating for the larger tires) i do an equal amount of highway and city driving. Is that within normal range. Lastly will installing a new cat, muffler system help or hurt fuel economy?