I would keep your eyes open for a set of one tons 14 bolt and Dana 60 if you want to wheel it hard, if not then it shouldn't be too hard to find a disc swap set for the rear.
If you are going for the axle swap then also figure what size tires you want to run and decide what gear ratio would be best for the set up and look for someone upgrading with the ratio you want.
if swapping you will most likely have to move rear perches since the swapped axle will come from a newer truck.
Really only two options.........................
1) Bigger axles, good upgrade but not always needed or wanted. But if your going 35 inches or bigger on the tires PLAN on it.
2) My front upgrade and swap in a 99 up disk rear end. http://coloradok5.com/forums/showthread.php?t=316597
, but it has been pretty good. I do brake a fair amount of hubs and as I type I am in the middle of swapping a front axle shaft because I broke the stub. But that is after 8 years of wheeling on 37 inch tires. The axle swap thing, although I know it's the right thing to do, puts a sour taste in my mouth because I had the axles to swap in and they were stolen. Does no one make strong axle shafts worthy of any type of wheeling? I have 35's on it now and haven't had any issues but I haven't taken it into the rocks yet. Another reason that I am reluctant to do the axle swap is That I have put a link suspension on the front with coil overs and got rid of the leafs and plan to do the same to the rear. I appreciate your input. Thank you.
) I have a million posts on that you can read about if you wanna hear me whine.