* 4L60E: This 4-speed automatic was very common.
* 4L80E: A heavier-duty 4-speed automatic, more likely found with larger engines or higher towing packages.
To know for certain which transmission is in *your* specific truck, you need to check one of the following:
* The vehicle's build sheet (if you have it): This will list the transmission.
* The sticker on the driver's side doorjamb: It may contain a RPO (Regular Production Option) code indicating the transmission.
* The transmission itself: The transmission case usually has a casting number that can be cross-referenced.
* Your vehicle's title or registration: Sometimes the transmission is listed.
Without this information, it's impossible to definitively say which transmission your truck has.