In a 2012 wrangler with automatic and the 3.6L Pentastar motor, 5:13's are going to be too low of a gear (numerically higher) and you'll be running 3000+ RPMs on the highway with 35" tires.
Another source from the FAQ: http://www.jeepforum.com/forum/f96/s...lator-1298121/
Which shows you engine rpm, speed and in which gear. Overdrive numbers (highway) are on the bottom row.
You can download an excel chart and play with the numbers. I still say 4:1 or 4:56 to keep your motor in a good efficient range for both power and best MPG.
Keep in mind, you're driving a brick on wheels. I would say 16MPG is fairly decent given you already have 35's. Best way to increase that is to take your 75-80MPH and drop it to 65-70MPH and enjoy the ride