fuel problems

[bigpapa1987]

ok i have a 87 ford f150 xlt lariat 4x4 and a 302 . it runs duel 19 gal tanks . i just replaced the rear tank sending unit and pump . also have replaced the high pressure pump on the rail and the fuel valve for the six lines . and i am still having the same problem . my front tank is over flowing out the neck and building pressure . also when i put gas in the rear tank it for some reason is being put in the front tank . i can have a haft tank in rear put the switch to front tank witch gas hand reads for it a day latter flip back to rear tank and my gas hand has moved down . the front tank stop working a long time ago but now since i replaced the rear tank i can have the switch on for that tank and it works. hope someone can help me with this