I have a 5

Yup. Why would I doubt you that someone said it's the computer?

The computer is the answer from everyone when they don't know how to diagnose the real cause of the problem. That goes back to the '80s and '90s when a large percentage of problems on GM products were solved with a new computer. First look for vacuum leaks. Pinch off various hoses. If one affects the idle speed, follow that one to its branches or the item it operates. You may also have luck spraying water on hoses and gaskets while the engine is still cold. Watch for a speed change or where the water gets sucked in.