Trucks has almost 200K doesn't burn or leak oil.

Oil pressure idling is around 40psi around 50psi when crusing on highway and only 70psi at WOT

 

sounds good to me

 

What would be psi signs to start worrying?

like idle 20psi for example
only 40psi at WOT etc

 

Maybe something like that, or so.

Shoot, a gen 4 truck with the oil pan reliefs valves installed in them are 25-30psi hot idle and 45-55psi at WOT. My old sierra that had 258k was 35-40 cold idle, 35 hot and was 45ish when cruising, 60psi at WOT.