Rich,
I would take your loader quick disconnects apart and make sure they are not obstructing the flow. The hydraulic flow on your tractor goes through your loader valve 1st, then on to your backhoe, and then on to your 3PH. That indicates to me that your problem may be between the loader valve and the loader cylinders. I would check the loader disconnects to see if something isn't restricting them. I hope this helps and good luck with it.