I recently bought an '08 Silverado 2500HD with an aftermarket radio in it, I got a factory radio coming from ebay, what do i have to do to get it to work in this truck? the replacement i have coming did come out of an 08 silverado

 

I may jsut plug right in. I depends on whether or not the Aftremarket radio has a plug-in adapter, or if the previous owner cut and spliced wires, which would be dumb, because most people won't wire it correctly for Onstar.

 

As nauticstar said, hopefully you can just unplug the aftermarket radio and plug yours in.
You will probably have to take it to the dealer to have it programmed if when you plug it in it says locked, or if the audio is too low or loud

 

it works perfectly. removed aftermarket stereo and the other part so onstar and chime would work. Installed an OEM radio i got off E-bay. Took it to the dealer, (where my buddy is the bodyshop manager so it cost me nothing). they programmed VIN to radio, Works perfectly. Thanks for help guys. I appreciate it.