Ford 4000 Position Control Issue

I just inherited a 1967 Ford 4000 3-cyl Diesel tractor with a new home. It was sent off to service just before the purchase so fluids were replaced. Everything is working well except for the three point hitch in Position Control mode.

The rear implement doesn't track the position control lever very well and drops, unless I have it set all the way up. It seems to raise the implement once I lift the lever above a certain point, but definitely not a linear tracking of the lever. Once at a height, the implement slowly drops the ground.

My initial reaction was to replace the ORings on the hydraulic piston, but I noticed that the implement maintains its position when the lever is fully up. If I raise the lever partially, the mower comes up but then starts to descend. If the tractor is off, and I lift the position control lever all the way up, the descent stops which leads me to believe the ORings are OK.

What else could be causing the position hold to malfulnction? It's almost like it's operating in draft mode, but there is a distinct difference between lift operation when I flip the control mode lever.

Thanks for any help.