I agree, Jim, that a good vent from the top of the tank to the filler neck is the rock solid solution for slow filling issues. That’s what Subaru uses.

Instead, I converted the fuel outlet on the round topped fuel level sender unit to an extra vent by drilling small holes in the tube near the top. I plumed that and the fuel pump vent to the charcoal canister, hoping that will be enough venting to allow a reasonably fast fill. If not, I’ll add the filler neck vent.
RPG