Case 1845c m91 tandem pump

At idle charge pressure is 50psi at full rpm it is 300 psi. When you stroke the levers forward or backward at full rpm it drops from 300 to 200. It also does this with the ports capped off that go to the drive motors so that I could eliminate there being leakage in those. Any thoughts? Also my pressures on the M ports that go to the drive motors are 4500 psi

Case 1845c m91 tandem pump