Warm engine, 1,000 rpm, 50+ psi, 4,000rpm, about 30 psi oil pressure.

 

This seems bass ackwards!   Is it a problem?

test with proper mechanical gauge to confirm.

If that is the case, you have very worn clearances in the mains r some other major oil system problem (oil pump relief?)

Hopefully it's a electrical malfunction with the sender or dash gauge.  wouldn't be surprising.  

I vote for screwy sending unit. 

GD

Oil level OK?  oil filter OK ?  any oil leaks ?

11 hours ago, GeneralDisorder said:

I vote for screwy sending unit. 

GD

+1.

Had to replace sender on my 87 GL a few yrs ago for same reason.

15 hours ago, GeneralDisorder said:

I vote for screwy sending unit. 

GD

Yeah.....likely.

That's why I suggesting putting  a test gauge on the pump to see if the readings are accurate, or if it's a faulty sender.