Biggest problem is info on HP increase's.
Welcome! I think you will find many options here... Look around, and you will find anything from 30 minutes mods (like a 4.0L TB) to a completely different approach to your engine (such as supercharging, turbocharging, or a complete rebuild like YJMechaninc did on his rig).
Let be the first to tell you, however, that the most bang for your buck for running those 33" tires will be to regear your stock 4.10 gears to 4.88... But then again, you might get bitten by the bug, and simply toss out the D30 and D35 and plug in some D44 with 5.13 gears like Bounty Hunter has on his rig!
Again, look around and you will find that most mods have already been tried by at least one member, so plenty of advice will be available. How much power you get out of the 2.5L will depend mostly on your wallet and how dirty you are willing to get your hands...
In my case, my mods are new ignition system (Performance Distributors rotor and cap, LiveWires, Sparkplugs gapped to 0.45, and Accell Coil), Ford Taurus fan (I strongly recommend this one!), synthetic fluids (oils and others), new (stronger) alternator, 4.0L TB bored out to 62mm with 62mm TB spacer, K&N filter, and removing the restrictors from the stock air box. With all these mods, you can start feeling a bit more power, especially when driving against the wind (where before I needed to downshift to 4th to keep up speed, I can now cruise in 5th), but nothing that will knock your socks off. As I said earlier, the biggest change will come from regearing (not counting the whole engine rebuild option or the Turbo or superchargers, of course). But again, if you ad a lot of power, you may be loocking for a new tranny sooner than you would like from what I hear (no experience here).
Felipe