I think the main issue you'll face with either 4.88's or 5.13's is that there is a pretty large mpg discrepancy between 70mph and 80mph. Ive got 5.13's and 35s. Cruise control on 65-70mpg i can average ~16mpg on flat highway. As soon as i kick it up to 80-85mph ill tank it right back to my city 13mpg. How you drive is more of a factor than 4.88/5.13(only in respect to mpg). I can say im glad i got the 5.13s because i have some resemblance of power to pass at 60mph. You'll probably be happy with 4.88s and 33's but any bigger and you're going to b dissapointed you didnt do the 5.13's.

 

When the superchip comes out for the 2011 u should definately get that but considering that u have 33' and not 35's I would go with the 4.88's. That way even if u go with the 35's eventually it would drive with some power as well.

 

Seems like regearing with autos is a balance between getting enough RPMs at highway speeds so that your transmission isn't coming out of overdrive (which really kills MPG from what I've read) vs. getting too many RPMs.

Looking at the RPM chart, the difference in RPMs between 4.88s and 5.13s is only like 120.

I don't have any real-world experience in this, but it doesn't seem like a big enough difference to really kill your MPG.

Also, what's your highway driving like? Do you have to deal with things like hills and headwinds that cause you to drop out of OD a lot currently?

I've got 35s, and an auto with 4.10s. I can get 18-21 MPG if I keep my transmission from shifting out of OD. (Which means I need to be going no more than 70MPH in a very flat area ... lol)

 

It can get rather windy some days, and we do have hills. It is not mountainous by any means, but definately some hills.

And also, when I am on the interstate, to keep with the flow I am going 75-78. So that alone, makes me worried about 5.13s.

I am looking for the best performance under those driving conditions, while not dipping below 15 mpg or so.

 

I can't wait to put on my nitto trail grapplers this friday! also will be installing a RC 2.5 spacer lift. I do a lot of highway driving. Please give me some advice untill i cant get new gears. I dont really understand the whole o/d on and off. SHould i get a procal or a superchips?
thanks

 

Have you found the RPM charts in the Drivetrain Faq's that were mentioned above? Plug some numbers in and see where your rpm's will be. Once you get the OD On rpm, divide that number by .69 to get your OD Off rpm. The mid-2k rpm range is where you want to be with this engine/transmission combo to have enough HP to hold speed without downshifts.

 

Where is the powertrain FAQ. Owners manual?

 

I don't have experience with 4.88, as I mentioned before I have 5.13's with my auto unlim and 315/70/R17's. I can tell you from my driving experience, that I have recently done some longer hwy trips of about 400 miles which included mountain passes....and I was going 75-80 mph the entire time, even held 70-75 up the steep mountain grades, and my avg mpg via the JK guage was 17 mpg and hand calculated I was right around 16 mpg.

 

Stickied at the top of this modified area

 

That is reassuring. I tried to run OD-Off this week, in hopes that it would give me 4.88 like power. It was much more enjoyable to drive, but I averaged 13 mpg