For the 4.0 motor it's at the power steering pump. There are two bolts on the back, the top bolt on the front, and a nut on the slider stud - all take a 13m/m wrench.
Once you've loosened those, put a 1/2" socket on the head of the adjuster bolt (runs crosswise under the pump, you may want to remove the airbox to access it easier) and play with that bolt - LOOSEN to remove tension, TIGHTEN to increase it.
Tighten all four bolts/nuts when you're done. The two on the back will certainly want a wrench, and you don't have to loosen them very far anyhow - so a socket really isn't needed for the adjuster bolts - just the crosswise slide bolt.
Be careful you don't crack the "knuckle" that holds tension on the pump - it's sintered, and I haven't been able to start making new ones out of wrought stock yet...
