There is no drain plug on the front carrier (atleast not on the 98-01 ones, I'd assume it's the same). The most economical and fastest way to get the fluid changed is to:
1) drive in 4x4 to stir up the oil
2) take a suction gun, suck it out the fill plug
3) fill with oil, repeat process till clean oil comes out.
If you ever have it out of the truck, drill a hole, helicoil it, and put a plug in it....