[drew300]

I had a bad rebuild once that gave the fault you have. Good cold, bad hot. I found that the main bearing clearances were too big, and that the pump was fine.
What to do ? I'd try some 50 weight oil and see if the pressure stays up. Not sure what to say about checking stuff. Does the oil pan come off without lifting the engine? If it does, you could check the bottom end, (plastiguage), and have access to the pump, if the bearing are good. But that still leaves the cam bearings suspect.
Hopefully others will write in. good luck