You still forgot to say if it is 1/2 or 3/4 or 1ton
Posi or open
Upgrades can't be suggested if we don't know what you are starting with.
Try something like this: Looking for a complete rear axle for a 2000 Sierra 1500 4x4, 3.73 gears, posi (if it has it), brake type (I'm not sure when they switched from drums to disks),
Much easier if you give too much info then next to nothing.
If you want to upgrade, what are you wanting to upgrade? Axle shafts? housing? Brakes? Gears? Locker? Rims? the whole shebang?
If you swap in a complete assembly from a heavier truck, you then have to worry about driveshaft length, matching gears to the front axle, mis-matched rims or custom axle shafts. If you broke a shaft, get chromolys. If you chewed the gears get better ones. If the posi doesn't work properly, get a good locker. If you are worried about bending the housing, get a truss.
There are so many variables to what you have, what (and how) you broke and what you want to upgrade it is almost impossible to give you a useful answer when the question was orignally not much more specific than "Looking for an axle for my truck"