won't pull past 5000rpm

[datdrift]

when under full load the motor won't pull past around 5 - 5.5 rpm.....i thought it might have been due to advanced timing, but now im thinking it may be down to lack of fuel getting to the engine the fuel pump has been making occasional strange noises so i thought maybe its on its last legs?? anyone have any ideas, it has had this problem since i have had it when it was running a non-intercooled 8psi but it seems to be worse now im pushing more fuel thru.
thinking about it i havent changed the fuel filter since ive had it so maybe this is partly blocked??? i need to change the oil so i'll prob grab a fuel filter off nissan at the same time and see if it makes any difference
any ideas