* 4L60E: A four-speed automatic transmission. This was very common.
* 4L65E: Another four-speed automatic, very similar to the 4L60E but with a higher torque capacity.
* 4 speed manual: A four-speed manual transmission was also available on some models, though less common than the automatics.
To know for certain what transmission a specific 2004 Silverado 1500 has, you'd need to check the vehicle's identification number (VIN) or look at the vehicle's documentation.
