There is no question we have run our Jeep JK through some really extreme trails and over every type of terrain. We are extremely happy with how the new vehicle has held up and haven't had any issues or problems with the JK's axles or differentials. This was a concern of ours since they were all-new designs, and usually it takes some time to work the bugs out.
The only real issue we've had with the vehicle is that we've been rolling around with oversize tires and factory gearing. As you know, this lethal combo has a negative impact on overall vehicle performance. One reason we had to wait so long is that no new gearing was available due to the JK's new design.
When Mike Denton Jr. of Superior Axle & Gear called us and said "Hey guys, I have some gears for you," we jumped out of our chairs and ran down to the shop. Finally! A set of 4.88s to offset the 35-inch Pro Comps. The Superior gears that are now available for the JK include 4.88 and 5.13 Dana 44 rear (standard on all models), Dana 30 reverse-rotation front (standard on non-Rubicon models), and Dana 44 reverse-rotation front (standard on Rubicon models).
It almost goes without saying that we aren't uneasy about using Superior gears and axles; after all, the company has over 65 years of manufacturing experience. Superior manufactures all of its products under the industry's highest standards.
One of the most common mistakes we find enthusiasts making when they modify their vehicles is that they neglect to change out their gearsets when running oversize tires. In some sense this is understandable due to cost, but in most instances you can buy the gears and have them professionally installed for less than $1,000. Swapping to the proper gear ratio significantly puts the factory performance back in any vehicle.
There are some minor changes in the JK's Rubicon axles. We really like the fact that Jeep included oil add and drain ports. A second change is the electric-locker connection, which is not difficult to disconnect. We suspect that if you are going to swap out your gears you know what you are doing, so we're not going to get into a full gear install.
We have run Superior gears on numerous project vehicles and can honestly say we haven't had a single problem with any set. So to bring your mileage and vehicle's engine performance back on track with factory specifications, we highly recommend you swap out your JK's gears after installing larger-than-stock tires on your new Wrangler.