Intake and exhaust are your best bets. But logic tells us that one really isn't all that good without the other...if you let it breathe in more by improving your intake, it won't help you if you can't get all that air out quickly. And the inverse is also true, why let it exhale if it has trouble breathing in?
But if it were me, I'd take the heads off, have them ported, polished or extrude-honed, and while you're at it, increase the valve sizes. Now that'll wake the thing up.
My older brother used to have a 94 XLT, and sold it a couple years ago to buy his 01 Mountaineer, and I was just talking with him this weekend, and he wishes he never got rid of it. He loved that truck, it went everywhere he wanted it to go, and never complained. He since sold his Mountaineer to my dad, who in turn sold me his 97 Eddie Bauer...keep it in the family!
Here's my other suggestions for you though: Throw some bigger, more aggressive tires on it, a little lift if you can swing it, maybe some new rims, a set of big round off-road lights on the bumper and a roof rack, and go hit some trails.
Best of luck to you.