if you dont have any suspension mods (i didnt see in your sig) then check the panhard bar. it needs to come off to get the differential out of the axle housing. i would start there. if you had gears installed, there is not much that needs to come off. panhard, driveshaft, calipers, and axles is about it. start with those pieces and eliminate them one by one.
another possibility is that the C-clips are not installed properly. this one will require you to pop open the cover, so you may need to purchase more gear oil, unless you can catch it all and keep it clean.