* Engine Code Variations: Even with the same engine code, there might be subtle internal differences (like piston design, camshaft profiles, etc.) between the 2000 and 2003 model years. These internal differences are usually not a direct problem for fitment, but may affect performance if significant.
* Mounting Points and Accessories: While the engine block might be largely similar, the mounting points for accessories (alternator, power steering pump, AC compressor) *could* differ slightly. These differences can require modification to the engine mounts, brackets, or accessory belts.
* Wiring Harness and ECM: The engine's wiring harness and the Engine Control Module (ECM) are *almost certainly* different. You'll likely need to either swap the entire wiring harness and ECM from the 2003 truck to the 2000 truck, or re-wire significant portions to make it compatible. This is a major undertaking.
* Exhaust System: The exhaust manifolds and possibly the catalytic converters could be slightly different.
* Transmission Compatibility: Ensure the transmission from the 2003 Silverado is compatible with the 2000 model's transmission.
In short, while the engine might *bolt in*, getting it to run correctly and reliably will require significant mechanical and electrical expertise and likely custom fabrication. It's not a simple "plug and play" scenario. You'll need to thoroughly compare the engines and their associated components before attempting the swap. Consult a mechanic experienced in engine swaps before undertaking this project.
