Fuel pressure dropping while driving and under acceleration to zero at idle runs 4 lb electric Blue

If I read your pics correctly, it seems the pump is ahead of the axle. That makes the feed line to it have to go up and over the axle.

Is it possible to put the pump behind the axle on the frame rail or somewhere else closer to the tank exit? That let's the pump not have to pull as much and should help it under higher-flowing conditions to be able to keep the supply flow/pressure up.