Will a 5.3 liter motor from 2005 silverado fit into 2000 silverado?

No, the 5.3L engine from a 2005 Silverado will not fit into a 2000 Silverado without significant modifications. The 2000 Silverado was produced before GM introduced the Vortec 5300 engine, so the engine mounts and other components are not compatible with the newer engine. Additionally, the 2005 Silverado uses a different transmission and computer system than the 2000 Silverado, so these components would also need to be swapped in order to make the 5.3L engine work.