Your lines were probably collapsing, lift pump pressure is making up for it. I dropped tank, modified pickup and vent then ran new lines to filter head and cp3. Made a huge difference, I had to turn my pump down bc it freaked out my FPR. Lol...
I know this again is an old post but did you run all new fuel lines or just a new line from the filter head to the cp3? Also do you think if I switched to a sump kit rather then my standard airdog install set up it would further resolve the problem?