* 4L80E: This is a four-speed automatic overdrive transmission. This was the most likely option.
* SM465: A five-speed manual transmission was less common but possible.
To know for certain which transmission is in *your* specific truck, you'll need to:
* Check the vehicle's documentation: The owner's manual or build sheet (if you have it) will specify the transmission type.
* Look at the transmission itself: You can find a tag on the transmission case that usually indicates the model number.
* Check the VIN: A knowledgeable mechanic or parts dealer can often determine the transmission type based on the vehicle identification number (VIN).
Without access to one of these sources, it's impossible to say definitively.