You have the dreaded "Fuel tank sending unit malfunction". Search for cheap fixes of the unit or buy it from Dodge for $72+ for replacement unit (here in NV, don't know about the east coast). Biggest decision is to drop tank or lift bed to access top of fuel tank and remove module. Moving bed is best from what I've read unless you have aux tank/toolbox, or like me a heavy shell w/accessories. Once they start to go bad they'll never be reliable again.
Chuck
Reno, NV