If you don't have the owner's manual, you can try:
* Checking the transmission dipstick: Sometimes the recommended fluid type is printed on the dipstick itself.
* Searching online: Search for your specific transmission type (often found on a tag on the transmission itself) along with "recommended transmission fluid".
* Consulting a parts store: A local auto parts store can look up the correct fluid based on your vehicle's year, make, and model.
Don't rely solely on general information; always verify the correct fluid type for your specific truck.