Signs of a leaky dif?
You could always drain the fluid out and refill with a thicker weight oil (like say 85w140) and see if that helps the problem.
can you got into more detail about the "banging adn hopping" at 45 mph? it only does it at a that speed? more details about the syptoms please

i've sent a few 10 bolts to the graveyard in my days and i never had one act up only at a certain speed or what not..if it was busted, it was busted.
did you get under there any check all your suspension?

