The label on the truck is more useful than a generic model maximum because trim, cab, bed, drivetrain and installed equipment change available payload.
Find the truck-specific labels
Look at the driver's door or door-jamb area for certification, tire/loading and occupant/cargo information. Wording and label arrangement vary by manufacturer and model year.
Subtract everything carried
Driver, passengers, tools, bed cargo, hitch equipment, aftermarket accessories and trailer tongue or pin weight all use available payload.
Payload is not the only limit
Also verify GVWR, front and rear GAWR, tire capacity, receiver or in-bed hitch limits, GCWR and the model-year towing guide. Use actual weights where appropriate.
General educational content for Canadian diesel-pickup research. Verify the exact truck, model year, certification labels, owner manual and manufacturer documentation, and obtain qualified mechanical or towing advice where appropriate.
Sources & Further Verification
Use the exact model year, VIN, truck labels and current manufacturer documentation when moving from general research to a purchase or towing decision.