Pull the tank sender unit and check the pickup filter, and blow out the lines. Old fuel can varnish the plastic sock bad. You can pull the unit without dropping the tank. Pull the tank drain and see what kind of crud is in the bottom. Put a vac pump on the line on the tank side of the filter and see what happens, using a brake bleeder attachment. see if the new filter is already clogged up with varnish crud. Check for rust dust in the fuel lines...

Not responsible for advice not taken...