Many (not all, certainly) will probably say that 5.13 is the right ratio for a 3.8 auto 4door running 35's.

The OD ratio for the 3.8 auto is .69

Using the chart in the faq's, you can plug in some numbers and make a few semi-educated guesses. You have 3.73's now, and we'll assume your tires measure 34". According to the chart, you are running appx 1781 rpm @ 70 with od on. Divide that rpm by .69, and you get 2581 rpm. Is that about where you're at when you turn od off right now?

So, looking at the chart, od OFF gives you the rpm of running 5.38 with od ON. With 5.13, you would lose about 120 rpm. With 4.88, you lose 240 rpm. With 4.56 you are struggling down around 2177 rpm @ 70. Ask yourself, is that enough rpm for you to hold OD...

I like my 3.8 auto running up around 2500 @ 70

 

Yes I run with OD off and I'm about 2500 - 2600 @ 70. I guess when I regear I'll go with 5:13. It was what was recommended by a parts supplier I just thought that was a steep jump. I didn't realize OD was that high. Is there anyway to change shift points. Trail dash 2 only will let you change WOT shift points.

 

Any reputable shops for regear in San Diego? Think I'll go with the 4.88s

mods, if there's a SoCal section that I don't know about please move this post. Thanks.

 

Down in the Staging Area, there are 3 California regional sections. Good place to try and hook up with locals for trail runs and install parties.

 

I had my gears done back in March on my 11' JKU... the BEST $$$$ spent so far...
I went from the stock 3.73 up to 5.13.. right now I am running 315/70r17 Duratracs (35's) and may go up to 37's in the future... I run 70mph, in cruise at about 2400-2500 rpm... It has power to get up and go from a dead stop and can actually PASS on the highway now...
If you want performance on and off the trail.. you may want to consider it....
I would STRONGLY suggest that you find a friend in your local club/group that is running a set up you are working towards and get them to take your for a drive.. (most jeepers wont let you drive their rig)... I went on quite a few rides before I decided...
big thing to consider is WHAT are you going to do to it in the future... bigger tires, lift, bumpers etc will all be factors... the weight starts to add up..
hope it helps...

 

I bought my 07 used, and the orginal owner installed 5:13 TeraFlex, and I am running 35s, with the overdrive on and pulling 60mph , I am running a little over 2000 RPM, I can live with that