deere loader problems fuel related

[imfixinmopars]

i have a deere 444h loader and when it sits overnite the pump loses prime?.it acts like the fuel drains back out of the ip?if you manually pump the mech pump it starts rough,then runs ok. i changed the filters,transfer pump,ck the lines,ect.what couyld it be? would it be a slight leak in the line fittings? the ip pump? help! ive got the loader sold and need it to be fixed soon.it runs good after it starts also,help guys,thanks...