New engine or not

okay, i own a 2000 wrangler with a 4 cyl 2.5. It's just lost its umph since it put on new tires and lift a few years ago. I attribute it to the piss ant engine just not having enough power. I don't want to go out and buy a new jeep, i just want it to havae more power, so I'm not forced to run in third gear in a headwind on a flat road. If i were to put a six cyl in, would that make a big difference and how much would that cost? would i need to put in a new tranny as well... seems like all of that would probably still be less expensive than a whole new truck??? please thought, opinions, cautions... thanks much

Putting the 6 in would take care of the problem, but would be alot of work. A better option might be to go to a reputable shop that could install a different axle ratio for you, that would bring your revs back to where they were before the bigger tires.