If you are still having curl issues....
Just how slow is slow when you say it slows down in the middle of the stroke.
Cause slowing down a little is normal. That's the geometry of the linkage. Similarly, where it is it's slowest (due to leverage/geometry) it is also it's most powerful.
As to the the other part to describe, about bucket not holding it's position when dumping to a backdragging angle....that's sorta referred to here on TBN as floppy bucket syndrome.
It's a sign of air in the cylinder. Now if you have something loose on the suction side, that could certainly introduce air into the system. But more often than not, it's a result of a loader valve lacking Regen function or an operator not using the Regen function if the valve indeed has it.
The loader, under gravity, tries to dump the loader bucket FASTER than the pump can fill it with oil. This sucks air in/draws vacuum on that cylinder and results in floppy bucket.
Try this to prove the point....dump the bucket ALL the way. Then once it's dumped all the way, hold the lever in the dump position for another few seconds. That will purge air out. Now curl back to the desired backdragging position and see if the bucket holds firm
