Low oil pressure at warm...why?

hi guys, i m andrea from Rome
i have 2nd generation vr4 1997 gto full rebuild but i have issue with oil pressure at warm
i have new oil pump oem and big oil cooler setrab buy while run my pressure is low.
i would like know hom many is the “good” pressure when run
when start to cold my pressure is near 4,5-5 bar…at warm 0,5…in running 1,5…
my tuner, to resolv this issue had changed my oil feed of my news 13g oem with smaller oil feed to increase the pressure.
this modification has broke the rear new oem turbo!
sorry for bad inglish