* TH350: This was the most common automatic transmission in those years.
* TH400: Less common than the TH350, but still a possibility, especially if it was a heavier-duty truck or had options geared towards towing.
To know for sure which one is in *your* specific truck, you'll need to check:
* The transmission case itself: There are markings cast into the transmission case that will identify it.
* The build sheet (if you have it): This would definitively state the transmission type.
* The vehicle identification number (VIN): A decoding service (many are online) can sometimes provide transmission information from the VIN, though it's not always guaranteed.
Checking the transmission case is the most reliable method.
