If you can afford it, I would recommend the dual cases first, and then the 4.7TS later for the above reasons AND, it is very nice to be able to shift to 2.28:1 in two wheel drive when arent quite to where you need 4WD. Depending on how your front end is locked, this can be more or less of an issue, i.e. easier steering. This just gives you more gearing options for going down the trail. With 4.7s only, you seem to be stuck deciding between highway gears and quite low. My
