Yes, that would be a huge difference.The link I put in has a good table of gear ratios and tire sizes and their affects on engine RPM.
The reason you feel a lack of power (other then the increased mass and rolling resistance) is because the engine isn't revving in its sweet spot of power delivery.
Installing taller tires like you have will drop the RPM's around 500 at any given speed. Different gearing can definately improve the responsiveness of the Jeep but it still has to push around a lot more unsprung weight. Its not going to be as peppy as stock no matter what you do.