[Ford-ferguson] NAA lift problem

[Tom Herman]

My NAA three point hitch is giving me problems.  Last year it quit lifting
with no load.  It would shake and shudder and very slowly come up about half
way.  I took the pump to my ford shop and they said they could find nothing
wrong.  So I removed the lift mechanism and had them look at it.  They went
through it but found nothing wrong.  I reinstalled and replaced it along
with the rubber washer under the acorn nut and screw (don't know what it is
called).  Cleaned the gunk and dirt from the valley and put in new oil.
Today the same problem reappeared.  Any ideas what my problem could be?

Thanks in advance.

TomH.