TonyG, your 3PH could have a leaky lift cylinder and be sluggish to lift a round bale. With the round bale lifted, if you shut off the engine, does the 3PH and round bale drop to the ground pretty quick or hold steady without dropping? This test will tell if you most likely have a leaking 3PH or low pressure.
Another thing, are you sure all your remotes are centered? Depending on system flow and priority, this could be an issue. Normally, the FEL is first in line from the hydraulic pump, but you just never know how a non-OEM loader might be plumbed.
The pressure gage will tell you some info about pressure, but it won't tell you for sure if it is the pump or something passing fluid back to the reservoir. If you had water in the fluid enough to make it milky, the system relief could have opened and be partially clogged so that it is not closing. That will reduce overall system pressure, but you should be able to hear it hissing and also it will get pretty warm.