Max towing capacity on a Rubicon Unlimited is 3500lbs.

If you are going to double that I would recommend a big truck or something more purpose built for towing. A JK is not the vehicle to tow what you are proposing.

I have a 2012 Auto with 3.21s and I just towed my camping trailer at 1000lbs on the interstate at 65-70. I can't imagine trying to tow 3500 let alone 7000.

 

Etars,
IMHO, my experience in safely towing isn't about the power and gearing to get the trailer moving but the braking and mass to safely stop the moving trailer. I was trailering a 3,000lb boat with a 2,000lb rated YJ and once had to evade an accident by going off a road when it was unable to stop in time on a rainy road. A replacement underwear incident. Couldnt imagine stopping my current 7,000 lb boat with my current JK. Be safe.

 

Instead of regearing, spend a little extra money and get a old work truck. 7000 lbs is to much for a jeep. I have the 3:73 with trailer brake and wouldn't pull 7000 lbs.