If you want to test the pressure in the hydro system you can buy a gauge online, reportedly for about $400. Or like a TBN member you can make your own for about $75 (see picture).
The parts used were: 1 x female Quick disconnect (QD); 1 x male QD; 1 tee, 1 elbow and a nipple and gauge (5000 lbs)
It is common for hydro attachments to bleed the pressure out when the engine is not running. Thus the loader will sink to the ground over a period of time, or the mower deck may settle also.