low oil pressure!!!!

[1helluva86]

hey,
i got a rebuilt 350 i put in my gmc. all new bearings, right clearances that i know of, new heads cam etc. etc. etc. heres the deal. At cold start it runs between 40-60 psi. at normal running temp, driving it gets anywhere between 30-50 psi. at a warm idle it drops to almost 0, more like 5 psi but instantaneously comes up when i hit the throttle. is this the bearings(which are new)? ive heard of oil filters causing this??? oil was just changed after the break in with no signs of metal really and there are no n oises fromthe engine.