* The owner's manual: This is the most reliable source.
* The fuel filler door: The capacity is sometimes printed on a sticker there.
* Your vehicle's identification number (VIN): A parts website or your local Chevy dealer can use the VIN to look up the specs for your specific truck.
Expect the capacity to be somewhere between 15 and 26 gallons, but don't rely on that range without verifying it for your specific truck.