Check out the last post in this thread.
Trouble filling gas tank past 1/2? - LX Forums Modern Mopar Muscle
From the thread, here are some of the possible causes.
The recirculation tube is plugged.
The usual cause for the hard fill condition is a restriction in the evaporative system hoses.Check for a stuck closed fuel control valve.
If spit back is the concern, there is a flapper door where the fill neck attaches to the fuel tank, if this flapper is not sealing properly it will allow fuel to come up the fill neck as the tank nears full. If this is condition is present a fuel tank is required to repair.
Comments: If a repeat concern is found where liquid is in the evaporative cannister and lines, The customers fuel filling habits should be reviewed.
filling a vehicle while the engine is running will allow liquid to be pulled into the evaporative system anything more than 3 clicks at fill up is overfilling the tank and can force liquid into the evaporative system