* Engine: The transmission must be compatible with the engine in your 1988 truck. Different engines require different transmissions. If you're swapping the transmission, you'll need to make sure the transmission's input shaft matches the engine's output shaft.
* Transmission type: There were various transmissions used in Chevy trucks of that era (e.g., 700R4, TH350, SM465). You need to identify the exact type of transmission in both the 1988 and 1991 trucks. Even if they are the same *type* of transmission, there might be internal differences.
* Bolt patterns and mounting points: While likely similar, there's a small chance the transmission mounting points might be slightly different between model years, requiring modification.
* Driveshaft: The driveshaft length might need adjustment because of even minor differences in the transmission's overall length.
In short, you need to identify the specific transmission in both trucks before you can determine compatibility. Checking the identification tags on the transmissions themselves is crucial. Even then, a mechanic specializing in older Chevy trucks should be consulted to assess compatibility and potential issues. Simply assuming they'll work together is risky.
