* Vehicle Identification Number (VIN): Decoding the VIN will reveal the specifications, including the GVWR.
* The sticker on the driver's side doorjamb: This sticker usually contains the GVWR and other important weight information.
* Owner's manual: The owner's manual should list the GVWR for that particular truck.
Without access to one of these sources, it's impossible to give a definitive answer.