i tried burping the system but not your way so i'll do that and see but i dont think it's air in the system.
and @AZP Installs what i mean by hard lets say i'm doing a quarter mile, when i'm half way through the needle will start to edge up. Only doing 180-200 does it move.
@Zander i changes by cap but think i'll try another one and there arent any clogs in the lines.
The water pump is brand new but it has two ports at the front, could it be one of the ports is not properly blanked off?