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) [TB] Discussion on pressure testing
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.