Jim,
You post further encourages me to think your valve is not operating properly. Think about it. The only time your fel should go up is when you move the lever to "up". Otherwise you spools are not working correctly. Especially from up to down. They are letting fluid flow into the "up" mode when it shouldn't. Some functions allow simultaneous movement of two directions, such as lift and curl or lift and dump. Also down and curl or down and dump. But they are plumbed to do that. I don't think that up and down are, since they are opposite movements.
If they could do that, which they shouldn't, your up and down would counter each other and the fel would not move. In your case the port with the least resistance is winning and letting a little more flow in that direction, but it is still being "fought" by the leak in the other direction. Hence super slow movement with the pump under strain. That would also explain the "tight" hose because the valve is trying to lift and exhaust from both ports. So your system is under pressure but the fluid has no place to go like normal, except maybe through the relief valve.
Maybe the restriction or wear is when you have the lever in full up position. As you pull it to get to the down position, it passes through that area where you said the fel works when feathered, or slightly on...which allows proper flow and function. That may be for a split second, but the fel responds to it and jumps up? My money is still on a bad valve or debris.