You have a PEX hose running from the FW tank to the pump. Can you see how high it is connected on the FW tank? Mine is on the bottom of the tank but I had one trailer where it was 2" up the side of the tank; making it impossible to use the full capacity.
Or, maybe a vent issue, but that's a wild guess.
Can you see the connections to your FW tank?
DW, 3 Kids and our Goldens
2012 Shamrock 233S
2008 Toyota Sequoia 5.7L 4WD