2003 2500hd rear diff problem

[Jeff H]

so i played in the mud the other day and ever since my transfer case has been leaking where it mates up the the tranny so i got to looking at stuff and i noticed that my u joints have a loooot of play in them so i changed them out but while doing this i noticed that my driveshaft has a loooot of play in it too about 1/8 of a turn that i can move it when the truck is sitting in N i dont know much about rear ends but im guessing that this is the pinion bearings going out? can someone correct me if im wrong and if im right how hard would changing these out be by myself,
thanks for the help