TN55 3pt problem

I have a 2003 TN55 with around 450 hours on it. I have had for about 2 years now and have experienced intermittant 3 pt problems. When I am either using my shredder or box blade, usually in the lower end of the 3pt range. It will get stuck in the down position, causing some serious headaches. It is not that big of a deal when mowing but when you are almost done grading the driveway or moving dirt and it buries the tractor it is a serious concern. In the past, I have been able to remove the current attachment from the tractor and jerk on the 3pt arms and it will magically raise back to the normal position. I have taken it to my local New Holland dealer twice but they have not been able to duplicate the problem.

Now I am having similar problems but now I can either fully raise it or fully lower it. It won't stay at any adjustment in between and it moves very slowly from the fully raised position to the down position. Any suggestions?