* Check the vehicle's sticker: Look for a sticker, often located on the driver's side doorjamb or inside the glove compartment. This sticker will list the GVWR.
* Check the owner's manual: If you have the original owner's manual, it will specify the GVWR for that particular truck.
* Check the VIN: Use the Vehicle Identification Number (VIN) to look up the specifications online through a vehicle history report service (like Carfax or AutoCheck) or a parts catalog. This is the most reliable method if you don't have the sticker or manual.
Without knowing the specific configuration of your 1988 Chevy C30, it's impossible to give you the exact GVWR.