* 4L60E: This was the most common automatic transmission. It's a four-speed electronically controlled automatic.
* 4L65E: Less common, but possible in some higher-output engine configurations. This is also a four-speed electronically controlled automatic, but with a higher torque capacity than the 4L60E.
To know for sure which transmission is in a *specific* 2001 Chevy Blazer, you'd need to check the vehicle's identification number (VIN) or look at the transmission itself (often a tag on the side of the transmission case will provide the code).
