I have TJ 2004, same engine as yours and I have 4 speed auto (don't know whether you have manual or auto). Also have Dana 30 and Dana 44 rear.
I am running 31x10.5xR15 BF Goodrich KO2 tires. I have 4.56 gears now, and it does not feel underpowered on highway at any speed. I get 2500RPM at 70MPH. Reaches 80MPH if it is not climb, but I try to keep it under 70MPH.
It will never drive like my 280HP Turbo Kia AWD 2021, but still does not feel a powerless at all.
Previously I had 3.73 gears and was a complete dog with 32 inch tires. Will get 2000RPM at 70MPH, which just did not work for highway speeds. With 33s, it would be barely drivable on highway.
As Jerry said, if you have 2006 Auto, you need 4.56 for 31'', 4.88 for 32'' and 5.13'' for 33''. After you have the right gearing as listed, try it, and see whether you still feel like you need to get stronger engine. I doubt that you will really feel a need for different engine with correct gearing. I definitely don't feel like doing stroker right now. It is not a sports car, and it was never intended to be one. 4.0 with correct gearing for your tires will get you anywhere you need, just don't expect it to accelerate too fast.
Don't listen to anybody you tells you otherwise for gearing ratios, they don't have a clue about the 42RLE transmission at it's 0.69 ratio overdrive. Before deciding on correct gearing, I should have spent bunch of time reading here, this way I would go to 5.13 with 33'' inch tires, and not to 4.56 which limits me to 31''. Even the Rubicon Auto was supposed to come out of the factory with 4.56 gears and not 4.10, BTW.