Those rear tires have an OD of just 27" and the stock 4 speed is a 1.0 final drive ratio. If you run 3.25 gears you'll be turning 2831rpm at 70mph. If you jump up to a 30" rear OD tire the cruise revs drops to only 2548rpm. If you drop down to 3.00 gears those numbers drop to 2613 (27's) and 2352 (30's) at 70 down the road. You've got to balance what you want for driveability, economy and performance.