Prochem Bear Cat Pump

Hi. my cat doesn't go to 1000psi any more!!!! stays at 200psi,I replace it and in the beginning was kind ok but only went to about 400psi but now the pressure regulator start shaking the most I get it's 300psi and is not working as it should be . New belts too. Any advice please
(I Replaced the pressure regulator too) I'm about to throw the towel