Do not assume. Check your owner's manual. It's the definitive source of information for your specific truck. If you don't have the manual, you can often find a digital copy online through the Chevrolet website or a third-party site specializing in vehicle manuals.
If you can't find the information in your owner's manual, look for a sticker or tag on the transmission itself. This might have a code or specification. Taking this information to a parts store will allow them to help you select the correct fluid.
Using the incorrect transmission fluid can severely damage your transmission. It is far better to spend a few minutes verifying than to risk costly repairs.