69 340 problems

Well the first thing I would do is eliminate everything prior to the fuel pump. Disconnect the line at the inlet side of the pump. Before you do that release any pressure in the tank and have something handy to plug the rubber hose. Hookup a line from the pump to a gas can with fresh gas and fire it up. If it's back to normal then the problem is from there back, perhaps a line sucking air. At least you would know which end of the car to work on.