While both engines are 5.3L, there are differences between the 2000 and 2004 versions. These differences may include:
* Engine Mounts: The engine mounts might be different, requiring modification or replacement.
* Wiring Harness: The wiring harness connectors and configurations could be incompatible. You'll likely need to adapt or replace the harness.
* Computer (ECM): The engine control module (ECM) will need to be compatible with the engine and the year of the truck. Simply swapping the ECM may not work. You might need to swap the complete wiring harness as well.
* Exhaust Manifolds/System: These might not bolt up directly.
* Accessories: The placement of accessories like the alternator, power steering pump, etc., could vary, requiring adjustments or replacements.
In short, while it's *possible* to swap the engine, it's not a simple bolt-in job. It will require significant mechanical knowledge and likely some fabrication or sourcing of parts. You'll need to carefully compare the two engines and their respective mounting points, wiring harnesses, and accessories to determine the feasibility and extent of the work involved. Consulting repair manuals for both years of trucks will be crucial.
