(were talking wrangler here just FYI) usually the 4.0's come with 3.73 unless its an auto, or a rubi (rubi's are 4.10), and the 2.5's come with 4.10's. with how bad the aerodynmics of jeeps are it takes alot out of the 2.5 to make it go down the road at the same speed as a 4.0. so while your running your 4.0 1/4-1/2 to go 75 the 2.5 is somthing like 3/4 throttle, so you don't gain much on the highway. around town is better than a 4.0's but... around town driving isn't usually high milage.