get a pressure guage and test the pressure either at the control valve or T into the pressure line and see what pressure it is getting at idle and also at high rpm.
you could have a problem in the relief valve or it could even be something as simple as a clogged sump screen/filter in the hydraulic tank.
i would check those 2 things to start with
good luck
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.