On CAT 320L I would like to rule out other causes before buying a pump. Hydraulics are slow
Before buying a new pump , I would get a Cat dealer to do a pressure test on your unit . Your may have enough pressure but just not enough volume of fluid to make the hydraulics work correctly . The pumps are variable displacement as are actuated by your pilot controls, It's possible that you pilot controls are not doing their job . I think it would be way cheaper to get the dealer to have a look as opposed to buying a new pump that you really don't know if it's bad .
I have been pressure testing - can't get over 4000 psi performed every test I can with service manual except flow, I was thinking maybe the main relief valve to get the pressure up
Just a thought. Have you changed the hydraulic filters recently and afterwards cut the old ones to inspect them for any metal particles in the filter media..?