No, a 2001 Dodge Cummins diesel transmission is
not directly interchangeable with a 2004 Dodge Cummins diesel transmission. While they might share some similarities, there are significant differences depending on the specific transmission (NV4500, NV5600, G56, etc.) and the specific application (single vs. dual rear wheel, etc.). The bolt patterns, bell housings, and even the overall dimensions can vary enough to prevent a direct swap.
You'd likely need significant modifications, potentially including custom adapter plates and driveline changes, making it a very complex and expensive undertaking. It's generally not a practical or recommended swap. You're much better off finding a transmission specific to your year and model.
