Changing the Axle seals and bearings isn't all that difficult but it requires some special tools like a slide hammer and adapter for knocking the bearings out.
I found this post on changing the bearings, it's for a Ford but they are basically identical.
One quibble, he says his axle looks fine but it doesn't look good to me, the bearing surface looks pretty bad to me.
http://www.f150online.com/forums/art...lots-pics.html