Are you talking about the radio? If so, "got'cha". General Motors has figured out a lot of ways to bleed money from you after the sale. One problem they had was their radios had a 100 percent failure rate and their authorized repair centers were grossly over-priced so peopled were replacing them with aftermarket radios. To counter that, they designed in the Body Computer into the radio so you had to get the original radio repaired and reprogrammed to your car by the dealer. Typical cost with diagnosis, removal, shipping two ways, repair, reinstallation, and reprogramming is around $450.00 for a cassette radio. Not a very customer-friendly process, but neither is GM a customer-friendly company.
After a few years the aftermarket industry comes up with ways around GM's nonsense. In this case what you want is called a "radio relocation kit". It is a long harness that lets you mount the radio in the trunk, but you can cut the speaker wires to connect to your aftermarket radio. I think there are additional kits that will allow some radios to work with your steering wheel controls if you have them.