* Transmission Type: The exact transmission type (4L60E, 4L80E, etc.) and its specific internal components differed depending on engine size, options (4x4, towing package), and year. A 1999 Tahoe might have a slightly different version than a 2003 Silverado.
* Bolt Patterns: Even if the transmission type is the same, the bellhousing bolt pattern (where it connects to the engine) may have changed slightly between the model years.
* Computer Control: The transmission's computer control and connections might not be compatible with the 2003 Silverado's PCM (Powertrain Control Module).
In short: You'll need to carefully compare the exact transmission model numbers (found on a tag on the transmission itself) for both vehicles. Even with matching numbers, professional assessment is highly recommended before attempting installation, as minor differences can lead to serious problems. Trying to force a fit without verification could damage the transmission, engine, or other components.
