77 f250 351m when i first start it oil pressure is about 60 psi ,as it warms up it goes down to about 10 psi.

put new oil pump in about 2 years ago,new lifters week ago,ran oil flush in it.

no knocking or pinging like when no oil is getting to parts ,only time you hear abnomarl noise is when you give it full throatal.

 

i
I'm thinking you've got worn bearings....and oil pump....

 

Is a sign of a tired engine, you can try thicker oil, 15-40, 20-50,