Check these articles and see if it's something you want to tackle.
http://www.moparmusclemagazine.com/howto/mopp_0308_mopar_rear_end_gears_set_up/viewall.html
http://www.carcraft.com/techarticles/ccrp_1006_mopar_83_4_inch_rear_axle_assembly/viewall.html
Search for Mopar 8-3/4 gear setup for more info. If you do decide to do it try to find someone experienced to check your work before you throw it back in the housing. After you've done a couple you will be good to go but the first couple are a bit tough to see if you've got it right or wrong.