Oil Pressure sensor (low readings)

I used Mani's is300 union bolt mod and when i first did the mod, my oil pressure would reach 5 - 6 on an fresh start up. but recently when i start up my oil pressure only goes to 1-2....So i thought my oil was low or bad, so i changed my oil and my oil pressure still only goes up to 1-2 on a fresh start up. And when driving on the freeway, at say WOT in 6th gear, going about 60 or so, my oil pressure doesnt even move. It only moves when i rev it pretty hard (60%).

What does this mean?

thanks
leonard