i had 27000 miles on mine when i swapped the rear gears. i replaced the bearings as well for added piece of mind. might as well do it while you are there.
+1 to bigcat.. had a gear change in a 99 with only like 50K on it and axels were ate up for some reason better change em it can't hurt em plus a whole bearing kit and all is around 80-100 bucks not bad considering the money it can save later!