While it has been a long time since I used any full size tractor, I remember two things. One, there is a speed control of sorts on the transmission housing on the same side as the hydraulic controls. See if that is adjusted to a slow setting. Two, I think whichever lever you are NOT using must be in the up position, though I am not sure about that.
Beyond that, I can only offer speculation. You might do a google search for clogged hydraulic intake on the Masseys. I've seen reports, forget where, that the lift arms have a grease point and that often overgreasing means the extra grease ends up in the hydraulic resevoir and tends to clog the intake. It's relatively simple to fix, apparently, but hard to access. Perhaps someone else has another answer for you, and if something works, please post back and let us know what happened.
Last but not least, and of course,