Hi and welcome to JA. The first thing that i would do is to change the hydraulic filter to verify that it is not the cause and plugged. But to do this you will need to remove the hydraulic pump to replace it and while you have it replaced you should check the pump to see if it is in good shape.
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The fluid is milky and my husband thinks perhaps we have an ice plug somewhere.
Also, it is a hydrolic/ transmission combination.
the manual shows that the pump is no where near the filter or even if there is a filter.It's a 65 or '66 diesel if that helps.