Is a 1999 silverado engine the same as 2002 engine?

No, a 1999 Silverado engine is not the same as a 2002 Silverado engine, although there might be some similarities depending on the specific engine. GM made significant changes to their truck engines between 1999 and 2002. While some engine families might carry over, internal components, computer controls, and even external dimensions could vary. You'll need to check the specific engine codes (e.g., 4.8L Vortec, 5.3L Vortec, etc.) for both years to know for sure if they're interchangeable. Even then, direct swapping might require additional work.