[sntrym95]

If the oil pickup screen was clogged pretty good initially, I would guess you have some cam bearing wear, due to lack of oil, to the point where the oil is flowing pretty good through there, but the clearances are just enough to not build pressure. You could go with a 10W40 oil which will help keep all the components lubed, but mileage will suffer and it's really only a temporary fix.

I have the same thing going on with a Vortec swap I just did and the engine guy is building me a new one to replace it.