Well, it's been a week now with the 5.38 gears in the Rubicon. Tires measure 33" tall. At 65mph, and Over-Drive working, I'm doin' 2200rpm's. About right I would think.... Gas mileage has actually came up a bit. Pulling the trailer in the pic, I was just barely 10 mpg. I'm gettin roughly 12 mpg now with trailer. Highway with trailer, well, before at 70 mph, it wouldn't shift out of 2nd. Now, it easily shifts into 3rd. But with the "tail" on the trailer, Over-Drive is useless. But was expected. Am about 3000 rpm I think it was in 3rd at 70mph. The little bit I did drive highway - Jeep only - it got up to 14 mpg. This is with the Flash-paq set on 87 fuel. These mpg's are from the dash readout - so take with take with a grain of salt... I have now set the programmer to the economy level and will see how it does. Will be mostly in town, as I don't usually get on the highway much. And will need to change programming to pull the trailer.

So, I've posted this info for anyone considering gears, and what to expect. Pic is front of my shop with trailer I pull for pickups and deliveries. I have had a car on the trailer too. Brothers Acura for one - when it needed hauled to Tulsa for the dealer to fix/replace the alternator and AC clutch and couldn't be driven that far. That was before I had the Jeep. Will post more info as/if I have some...
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I don't know much if anything about gears. Why did you go with 5.38 instead of 5.13? I always read about most people using 5.13s. Just recently I have seen more people started talking about the 5.38s, but I thought that was for 37+ tires. Or does that depend on auto vs manual? I know I need to regear at some point so I liked your post.

5.38s will give a bigger mechanical advantage putting power to the axles & thus the wheels. 5.38s didn't come out until recently (last year or so).

testrat would see the better gains in mpg if he had 35s. but I would guess he got the gears primarily to help with the towing. Also, with 33s and 5.38s, he should be able to crawl like a mofo with the tranny in 1st and the tcase in low.

I'm running 4.88s and 315/70r17s (~34.5") on an auto and I'm averaging 15 mpg combined hwy/city driving.

Since I have this trailer to pull around, I needed the power, and a post somewhere I read where a guy was comparing auto to manual - noted that the Over-Drive in the auto trans was geared slightly higher. So I had hoped to get back some from that. Another post - one gut had 5.13's and wished he had 5.38's. Another had 5.38's and loved them. Don't know tire size of either. But all were JK's. And I gave the measured tire size, instead of: 315/70r-17 - kinda WTF is that tire size. Actual size makes more sense. At least now, it shifts out of 2nd at highway speeds with the trailer. And the tailgate - I made from scratch, as I didn't like the gate that came in it. Was too heavy to get off and on. So, I made one that I can pull the top half off and reduce the wind load or can also pull the bottom off also, then you hardly know the trailer is there. Now, I just need to figure a way to store the sections when off. Gotta build some sorta rack under the trailer to slide them into and lock in place. Another project... Gettin' a bit long here, so I'll quit here...

Wow, your 315s measure only 33". mine measure ~34-1/8" in the rear and ~ 34.0 " in the front at ~35 psi. Firestones website says the Destination MTs measure 34.4x12.7" on a 17x9.5 wheel. So I was pretty suprised when the actual measured size was pretty close. Still, I wish it was closer to a true 35" tire

but that trailer looks HEAVY loaded the way it is. Suprised our mini van motor can handle it

Oh the 5.38s being new explains why I haven't seen much about them. I am currently running 35s on my stock 3.73 gears. It is fine but I do want to regear. Glad I asked the questions cause I was still thinking 5.13s was the way to go. Of course either would be way better off than my stock gears.

My stock gears were 4:10's. Just for reference. So, wasn't too much of a step for me... Don't know if the Rubicon JK package is different from none Rubi's..