You'll need to consult your owner's manual. This is the definitive source for the location and specifications of all fuses and relays in your vehicle.
The owner's manual will have a fuse and relay panel diagram showing the locations and functions of each. The diagram should clearly show which fuse and/or relay are responsible for the fuel pump circuit.
Without knowing the specific engine type and having access to your owner's manual, I cannot give you the precise location. Searching online for "2004 Dodge 3500 [Your Engine Type] fuel pump fuse" or "2004 Dodge 3500 [Your Engine Type] fuel pump relay" might yield some results from forums or repair manuals, but always double-check against your owner's manual.