No doubt it's more complex than this, especially concerning Chassis-Cab models, and the C3500HD. I've never seen underneath, or laid a wrench on either one.
Otherwise, GMT400-family swaps:
2WD rear axles swap into 2WD chassis.
4WD rear axles swap into 4WD chassis. Match front and rear differential gear ratios.
If you change the number of wheel studs--5-lug to 6- or 8-lug, 6-lug to 8-lug, or whatever, you'll need different wheels or some craptastic "adapter/spacer" which then loads the wheel bearings differently due to the wider track width.
If you change gear ratio, you'll also need to deal with speedometer and potentially other vehicle-speed issues unless the gear ratio change is offset by a tire-circumference change.
Things will get more complex if you change from single rear wheel to dual rear wheel.
There is the potential to screw-up brake balance if the replacement axle has significantly-bigger brakes than the OEM axle. 254mm/10" upgraded to 11.x is a nice improvement. 254mm to 13" may not be.
SUVs may have rear sway bar mounts. A pickup axle can swap into an SUV, but you'd lose the rear sway bar which can upset handling. An SUV axle can swap into a pickup, either don't add the sway bar; or modify the vehicle to accept it.
GM is notoriously stingy with locking or limited-slip differentials. Verify before purchase to assure you're getting what you think you're getting. My '97 K2500 had a snow-plow mounted on the front when I got it; but had an open rear differential until I put a TrueTrac in it.
Anyone: Corrections or additions?
Otherwise, GMT400-family swaps:
2WD rear axles swap into 2WD chassis.
4WD rear axles swap into 4WD chassis. Match front and rear differential gear ratios.
If you change the number of wheel studs--5-lug to 6- or 8-lug, 6-lug to 8-lug, or whatever, you'll need different wheels or some craptastic "adapter/spacer" which then loads the wheel bearings differently due to the wider track width.
If you change gear ratio, you'll also need to deal with speedometer and potentially other vehicle-speed issues unless the gear ratio change is offset by a tire-circumference change.
Things will get more complex if you change from single rear wheel to dual rear wheel.
There is the potential to screw-up brake balance if the replacement axle has significantly-bigger brakes than the OEM axle. 254mm/10" upgraded to 11.x is a nice improvement. 254mm to 13" may not be.
SUVs may have rear sway bar mounts. A pickup axle can swap into an SUV, but you'd lose the rear sway bar which can upset handling. An SUV axle can swap into a pickup, either don't add the sway bar; or modify the vehicle to accept it.
GM is notoriously stingy with locking or limited-slip differentials. Verify before purchase to assure you're getting what you think you're getting. My '97 K2500 had a snow-plow mounted on the front when I got it; but had an open rear differential until I put a TrueTrac in it.
Anyone: Corrections or additions?