For that kind of a use case, you really don't need to change out the axle/brakes.
That said, if you want to make an upgrade just because, there are a few options available.
I personally put a 3.73 rear end out of a grand cherokee in the back and a disc conversion from Speedway on the front.
The 4WD S10 rear end is another popular choice for the rear. There are a few different choices, really. Though there are some other changes that you might consider at the same time.
If you want to go down that rabbit hole, I would recommend starting a thread over in HiPo to explore it.
