* Computer Control: The transmission's electronic control strategy changed slightly over those years. The 1999 transmission might have a different PCM (Powertrain Control Module) interface than the 1996 Tahoe's computer. This could lead to shift problems, improper operation, or even damage if they aren't fully compatible.
* Internal Differences: Though generally the same, there could be minor internal differences in valve bodies, torque converters, or other components. While often interchangeable, these slight differences aren't guaranteed to be seamlessly compatible.
In short: It's *likely* to work, but not guaranteed. The swap *might* require a PCM reprogramming or even a complete transmission controller swap to function correctly. It's best to check the specific part numbers on both transmissions and possibly consult a transmission specialist or a reputable transmission parts supplier to confirm compatibility before proceeding. A simple bolt-in swap isn't always certain.
