Fuel Prssure Issue. need help

Hey whats up guys. Im new here. I have a fuel pressure problem. My fuel pressure duty cycle will not go past 50% performance. once it hits 50 the fuel pressure starts dropping at WOT(at about 4000rpm). I cant get it fully tuned because of this issue. the Duty cycle should perform up to 100% to maintain fuel pressure at about 39lbs. I have a boost a pump, 42 lb injectors, focus pump. let me know what you think.

fuel pressure issue

hmmm. didnt think about the fuel filter. Ill check it out. The fuel pressure is between 39-41 i think, up till i hit about 4000-4500 rpm and then starts droping to 24-26 range. My voltage is a little low. im at about 13.4. it has been a while since i played with it. Wells heres another factor. I had the same setup with a factory motor. it was running fine and was able to tune. I then swapped motors and bolted everything back on. When i tried to get the new setup tuned, they didtnt want to tune past 4000 rpm cause thats when fuel pressure droped. Do you think i may have crosssed vacume lines or would that not make a difference ? The vehicle is a 2003 gt, w/ 42lb injectors, saleen supercharger and minor bolt ons. i do have the battery located in the trunk but a i ran a 2gauge to the front and ran a separate cable to the starter.