* Transmission Control Module (TCM): The 2002 4L60E likely has a different TCM than the 1998 Silverado. The TCM is the "brain" of the transmission and needs to be compatible with the truck's computer system. You'll likely need to use the TCM from the 1998 truck, or possibly have the 2002 TCM reprogrammed. This is a significant hurdle.
* Wiring Harness: The wiring harness connectors might be different between the two years. You might need to modify or replace parts of the harness to make the connection.
* Input/Output Shafts: While unlikely, there's a small chance the input or output shaft splines might be different, preventing it from mating with the engine or driveshaft.
* Valve Body: Internal differences in the valve body could exist, though less likely than TCM compatibility issues.
In short: While the transmission is the same *model* (4L60E), the internal components and especially the electronic controls have likely changed enough between 1998 and 2002 to create significant compatibility problems. It's not a simple bolt-in swap. You'd need a knowledgeable transmission specialist to assess the compatibility and the work required. Finding a used 4L60E from a 1998-2000 Silverado would be a far safer and less costly route.
