58 dodge pickup with a stock tank, 413, mechanical fuel pump. Ran great, had a problem with the fuel tank pressuring when hot and leaking gas out the pickup fitting. Vented the gas cap to resolve it, and now it runs fine when cold, but as soon as it warms up and is driven, the fuel filter runs bone dry. Checked for vacuum leaks on the line from tank to pump, found no loose fittings. Any ideas before I throw in an electric fuel pump?