* Most Likely: The 1989 Chevy Silverado 1500 with a 5.7L (350 cubic inch) engine would most likely have a TH700R4 automatic transmission. This was the standard transmission for this combination in that year.
* Less Likely: While less common, there's a slim chance it could have a 4L60E automatic transmission. This transmission started appearing in some vehicles around this time, but was generally more prevalent in later models.
How to be sure:
* Check the VIN: The best way to determine the exact transmission is to look up your vehicle's VIN (Vehicle Identification Number). You can find this on the driver's side dashboard or on the driver's side door jamb. You can then use the VIN to access online databases or contact a dealership to get the specific transmission information.
* Look at the transmission itself: If you can access the transmission, you can often identify it by its case and markings. The TH700R4 and 4L60E have distinct markings and physical characteristics.
Note: There is a chance the truck has been modified, and the transmission may not be original.
