The JK engine needs around 2500 rpm to produce sufficient rear wheel horsepower to operate efficiently.
Here is the torque and horsepower curve comparing stock to a Superchips 91 octane tune:
Notice how steep the lower, rear wheel horsepower line in the graph is. Stock rear wheel horsepower at 2000 rpm is only about 60 compared to the Superchips tuned rear wheel horsepower at around 2800 rpm is over 100, and at 3000 rpm it is about 110.
Stock torque at 2000 rpm is about 150 and the tuned torque at about 2800 rpm is about 190. At 3000 rpm it is over 190.
Those increases from 60 rear wheel horsepower to 100+ or 110+ rear wheel horsepower and 150 torque to 190+ torque are quite meaningful.
So, if you are concerned about the power capability of the JK engine, the first thing you want to do is make sure your wheel/tire/gear combination puts you at over 2500 rpm at highway speeds.
Next is a chart of rpm levels by gearing and transmission type at 70 mph:
You would need 5.13 or 5.38 gears with stock size Rubicon 32" tires to put you at 2600-2700 rpm with an automatic. Essentially, this means that any larger tire on an automatic will put you at the lower end of the horsepower and torque numbers--even with a regear.
However, a stock 6 speed Rubi with stock 32" tires in 6th gear puts you over 2500 rpm at 70 mph. 4.88s and 35" tires (that actually measure 34" mounted) puts you at around 2800 rpm at 70 mph.
So, due to transmission gearing, with 4.88s and 35" tires you can run in a better power range than stock.
With larger tires, you need better than stock power because you are turning heavier, larger tires.
Also, lighter tires will help with performance. For example, load range C 35x12.50R15 tires on aluminum 15x8 wheels are significantly lighter than load range E 35x12.50R17 tires on 17x8 steel wheels.
With 5.13 gears, a 6 speed, and 37" tires (actual mounted height around 36"), my 2 door JK Rubi would run around 2800 rpm at 70 mph. I could drive most any freeway grade at 3000 rpm with my Superchips tune because that put me in the 110 rear wheel horsepower and 190+ torque range.
Whereas a stock automatic JK has no chance of driving a steep freeway grade without gear hunting/constant downshifting because they are running less than 2000 rpm and less than 60 rear wheel horsepower. Then, add heavy, larger tires/wheels to the equation with no tune or regear, and the people who you may have spoken with that suggest that you feel you can almost walk faster are right.