Try these two links for info on axles.
<a href="http://www.off-road.com/jeep/tech/axle/" target="_blank">More axle stuff</a>
<a href="http://www.off-road.com/jeep/swb/articles/specgrid.htm" target="_blank">Axle stuff</a>
Just read the tag on the front axle; it should tell you. The AMC 20 is a little more tricky because it uses a code. I believe mine says B on it and that is a 3.31 ratio.
2004 Rubicon, 6" lift, 35s, winch, hard top, full doors, bumpers, tire carrier and rock sliders.