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I have heard of filler necks not venting properly... if you look at the filler neck, there is a little vacuum line looking tube that dumps out... I guess that could be a place to check. see if anything is blocking it?
Mine does the same thing. What i have determined that is not a breather problem its is a flow problem into the tank. Something to do with the how the fluid goes into the neck sets off the pump. I have also found that holding the pump head sideways solves the problem for me.