* 4L60E: A four-speed automatic transmission. This was very common.
* 4L65E: Another four-speed automatic, a heavier-duty version than the 4L60E.
To know for certain which transmission is in *your* specific 2000 GMC Jimmy 4x4, you need to check the vehicle's identification number (VIN) or look at the transmission itself (often a tag is visible on the side). Your owner's manual will also specify the transmission type.