Hi and welcome to Just Answer!.
It sounds like you need a fuel pump. That sounds pretty simple, but let me explain...
The fuel tank on your Pacifica is a saddle type unit, something split in two by the need for a rear driveshaft on the AWD units whether you have this or not.
Filling the vehicle means you spill fuel into the left side of the tank, which then transfers to the right as fuel levels exceed about 3/4.
Since any fuel level below 3/4 means the sides are isolated, there were provisions made to move fuel from the right to the left, which is where your actual fuel pump lives.
This is done by using an ejector system. Fuel pump output to the engine
is sent from the right to the left side of the engine, with any excess fuel being diverted to an ejector that sprays a strong jet of fuel through an orifice that is connected to the left side of the tank. Normal operation means more fuel is transferred than is used, so excess fuel on the right side tank is shuttled over to the left if things work properly.
In the case of a weak pump, you'll have less ejector spray, which means fuel transfer from the right side simply doesn't happen. The crazy thing is that the fuel pump is still healthy enough to sustain normal engine functions but isn't robust enough to get fuel moved from the dead side of the tank to the other. The result is that the left side goes dry and the refuel process can hold only a small portion of what the tank is rated for... since the right side still has plenty of fuel in reserve.
It does get complicated! I fell head over heels into this trap on the first Pacifica problem of this nature, mistakenly replacing the right side fuel module since it seemed to have the deciding factor for fuel transfer... and there were no running problems otherwise. It took a scale mockup of the actual parts immersed in fuel to show me what the problem was.
I believe this to be the same problem.
Let me know if you have any questions... I'll be glad to help.