1990 Chevrolet K1500 350/5 speed regular cab longbox.

The door sticker only lists GVWR (5600) and GAWR (3400 each front and
rear) with no GCVWR.

The manual and the shop manual both tell me "ask a dealer."

It's my father-in-law's old farm truck... it's done a lot of towing, but
I have no idea what it's actual towing rating was.

Does anyone know? :)

Ray