Is that oil temperature or coolant temperature?
IMO.
30 psi at idle is on the high side, but considering the engine if the oil is only at 180 F, not out of line.
50 psi at 3000 is OK.
Going down with increasing rpm is not OK.
^ This suggests insufficient flow into the bearings.^
> Some possibilities are:
1. Loose or worn bearings. More oil is needed to support a worn bearing and the amount of oil needed for bearings go up with rpm.
2. Oil pump not supplying enough volume.
3. Pump is supplying enough volume, but weak relief spring is sending a large proportion back to pan.
4. Pump is supplying volume, but viscosity is too high and opening the relief spring. Not enough oil flows into the engine to keep up with rpm.
------------------------------------------------------------------------
I should add. While it is possible for flow not to keep up if the oil is too thin, that doesn't seem to be this situation. That's more likely on a hot running or heat soaked engine. Because even if 180* is coolant temperature, its likely the oil temperatures are in that range because its not like you were road racing or pulling a trailer.
For example:
Rotella T 15W-40 had a viscosity around 24 cSt at 180 * F.
A typical SAE 5W-30 or 10W-30 would be around 16 cSt at the same 180*F. With normal clearances etc, we know that viscosity is about right for an original engine as well as most aftermarket.
For comparison, if the engine's oil was about 230*F (110 *C) then the 10W-30 might be a bit thin as it would drop to 9 cSt.
And at the same 230*F, the Rotella 15W-40 would be about 12.5 cSt.
So this is why I don't think the oil is too thin unless the bearings or something further downstream is loose or worn. I've had engines with worn bearings. The heavier weight oils are only a partial help. Same with a higher volume pump. I hope thats not the situation here.