If you have changed the hydraulic filter and still have the problem then, pull the left rear foot plate loose on the back and you will see a round access cover that will go into rear axle housing. You will see the suction pipe that is bolted to it-take the bolts out of that pipe and get it out of your way. When you pull the round access cover, inside attached to the cover is the internal suction screen-if it is really clogged up you need to rinse and clean the entire housing internally-we have even had to remove the lift cover to clean it properly. Some tractors came from overseas with some type of additive that "slims" in the hydraulic fluid.
I will send you a PM.