Okay, time to get dirty!
Put the parking brake handle down. Jack up the rear wheels. Crawl under the Jeep, above the driveshaft you'll see the parking brake cables (one to each rear wheel). Follow them forward until you come to a T attachment, where the two cables go to a metal bar, and attached to that bar is one cable (which goes to the handle) If you look closely you'll notice that there is a threaded shaft on this single cable, behind the T bar are two nuts, a lock nut and an adjusting nut. Just back the lock nut off and then tighten the adjusting nut. Every now and again get out from under the jeep and pull the handle, how's it feel? Also, when you have the brake set to where you like it make sure that the wheels turn freely when the parking brake is off.
Personally I like to adjust it to where the handle will only go up halfway, that way you can pull the brake in an emergency and it'll stop you (if you ever do this be very careful as it will lock up your rear wheels quickly.
Sequoia