If you haven't changed the diff gears to match the tires that you are running, that should be your first choice. Otherwise it looks like it will run you about $1200 to add a 4.7 gear driven t-case to the V-6 transmission.
In the mean time if you have A/C, you can kick it on to help with descents/drop offs when crawling and if you turn up the idle screw you can reduce a lot of stalling while on the trail. It wont be the same as dual cases or 4.7's, but I found it helpful.
