If it was an American built truck it should have a GMC V6 in it. Canadian built GMC trucks came with the inlines. You should be looking under Chevrolet to spot that carburetor.
http://www.autoline.ca/service_locations.htm This is the company we deal with. Most of these carbs share the same rebuild kit. If the aluminum tag has come off the top of the carb, you might see a casting # on the base.