Maybe double check your vent line? Almost sounds like you have an 'air lock' situation that perhaps a 'full' tank overrides easily, but a 2/3 full tank does not.
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Rich
'09 Keystone Fuzion FZ403, Touring Edition, 244 of 300.
'08 Chevy Duramax
Full-time in my Fuzion since 2011
USAF Vet. B-52G Crewchief.
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