* SM465 4-speed manual: This was a very popular heavy-duty manual transmission.
* TH400 3-speed automatic: A common automatic choice, known for its robustness.
To know for certain which transmission is in *a specific* 1988 Chevy 3500 4x4, you'd need to check:
* The vehicle's documentation: The owner's manual or build sheet (if available) will specify the transmission.
* The transmission itself: Look for markings on the transmission case.
* The VIN: A dealer or mechanic can use the VIN to look up the original specifications.
Without more information about the specific truck, it's impossible to say definitively which transmission it has.
