Reviving this old thread. Just about to order my 4.56 gears. Just to be sure, I did some more research to make sure I didn't want to go to 4.88's. I really don't do much highway driving above 70 Mph, so it almost made sense, but in the end I decided to just stick with 4.56.
I found the following web site incredibly helpful to making the decision: http://www.4ws.com/gear-ratio-rpm-calculator
It allowed me to drop in the most accurate gear ratios I could find for first-thru-sixth gear. I put in my measured tire dimension of my new 37" tires, and then compared that to my old 35" tires in terms of what I was feeling, and then just kept bopping between different gears to see where things landed. With my old 35" tires, I was moderately happy with my 3.73 gear ratio. I kept feeling that it could use a bump to 4.10, but overall I could handle 3.73. I see that with my 37" tires, at 4.56 gearing, I would be slightly higher in gearing than my 35" tires at 4.10 gearing, so that ended up being the deciding factor for me. I think that 4.88 would have just been too tall. I have found out that Chrysler seems to have changed sixth gear from the 0.83 gearing that is often quoted to 0.797, so if you use the link provided above, make sure you double check the numbers from the built-in "Pre-Filled" drop down list, as those numbers do not appear to be 100% accurate.
Here is what the tool was showing for me between the 4.56 and the 4.88 gearing.
4.56
4.88
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