Yes, you can get 180hp with a bolt-on supercharger. The downside is that you have to run Premium instead of Regular. That's a problem with all higher compression engines though.
150-160 is more reasistic with cheaper bolt-ons like headers, hi-flow cats, catbacks, ignitions, porting, 4.0L TB, TBS, electric fan, etc... You also have to take into consideration where you want the power. You can gain more HP if you're willing to loose low end torque. Most bolt-ons are either designed for mid to high end power.
The problem with gas mileage and performance is that it gets offset once you start lifting and adding more weight to the Jeep. If you kept the Jeep mostly stock (31's or less) and add bolt-ons you could see a decent improvement.
Remember you'll want to regear for any larger tire to take full advantage of things.
Also, a 9lbs inertia ring would probably be a good choice. What it does is adds more weight to the rotational mass of the flywheel. This keeps the engine turning without loosing as much speed when under load. THis would help on and offroad.
Keeping your highway speeds down really helps but isn't always possible. Staying under 65mph, will give you better gas mileage then if you went over.
Depending on how you set up the Jeep, you could see anywhere from mid teens to mid twenties. There are a few who have documented as high as 25-7 but those are dependant on many factors.
Short trips, I think the 2.5L does well. Geared right, longer trips can be done. If you do a lot of highway stuff then a 4.0L might be a better option. If you're mechanically inclined, you could buy a cheap 2.5L and swap the engine.
Any reason you're wanting a TJ and not a YJ? If it's the suspension, that can be fixed with some tweaks. Also, considering the price difference, you could probably buy a decent YJ and a lift kit for the price of some TJ's. Just a thought....
