no fuel to fuel rail

maybe the fuel pump. And it does have a relay so you did the right thing there

They are about 120 bucks

After verifying that no Fuel Pressure exists, check that the Fuel Pump is getting power (12 Volts). This can be done by tapping into the power circuit that feeds the pump with 12 volts with a Multimeter (but without dropping the Fuel Tank to remove the Fuel Pump). Once you're tapped in, have a helper crank the Engine while you observe your Multimeter in Volts DC mode. If Voltage is present (12 Volts), then you have confirmed that the Fuel Pump Fuse and Fuel Pump Relay are working perfectly. If your Multimeter registers 12 Volts... you can replace the Fuel Pump with confidence.

use jumper wire from verticle slots in relay box. This will independently run fuel pump. It no pressure then fuel pump or wiring to fuel pump is faulty. Make sure you have current in the slots while testing.

i have 1998 dakota 4x4 3.9 doing the same have replaced complete fuel assembly twice now. I get about 5 seconds of 12 volt to the pump . I have swapped out shut down relay starter relay and fuel relay. As soon as pump kicks on seems to shut down, no pressure at the rail.Some times if does run will just shut down as if shut key off (may restart may sit on road a while. I have also replace crank sensor , pick up coil , IAC , and plugs. Would like to know your findings