With the 4.56 gearing lil monster is screaming doing 75 and I average about 4 mpg less per tank than the OE 4.11
But that low end.... man she can chug up a 10% (guesstimate as I have no clino) hill in 2nd with no issues. albeit very slowly.
I would definitely be interested in the real world effects from the 4.88 you have on your JK.
TheKnewb,
After three years of running stock, and averaging 20mpg @ 70mph & 2300 rpm on the highway (cruise control), I finally decided on a 3" lift with 35's.
**Oh, just FYI, my rig is a 6 speed manual transmission**
First, I ran like that for about 2-3 weeks with plenty of 100+ mile trips on the highway in that span on the 35's. My mpg dropped significantly to around 16-16.5 mpg @ 65mph & around 2800rpm. That was he reason I bought the 12 gallon Titan tank vs the Jerry can set up. I was afraid of not having enough fuel for overlanding.
Secondly, I decided to buy the Superchips
Flash Paq and reprogrammed the speedometer and to 35" tires. That alone return my mpg to 18.5-19 mpg @ 70mph & around 2800rpm, on a 150 mile freeway trip.
Then, after many days on forums, talking amongst friends I decided on 4.88's.
Now, I average 17.5-18.5 mpg @ 65mph & 2500rpm.
All these tests came from 80-100 mile trips to visit friends in the Inland Empire. Always being on cruise control and very very rarely slowing down and or speeding up.
Now, on the surface streets, with 4.88's, I average about 16mpg @ 25-40 mph. There is definitely a lot more shifting at lower speeds on the surface streets. But I have been driving stick shifts for 15 years. Doesn't bother me.
On the trail......latest trail was the Rowher Flats. Pretty steep climbs and decents at various parts. BOY an I super satisfied with the 4.88's.
Sorry about the long write up, hope i covered everything and that it helps.