Do you know if the hyd pump is pumping full volume as in GPM.
Are you using max engine rpm?
When you are moving the FEL/curl, is the 3pt lever in the neutral position , so as to not cause back pressure. If you have a pressure gage in a tee in the IN port of the FEL, you can determine the pressure for any hyd application.
If you max out the cyl, you should read the relief pressure.
If you only work the 3pt, you will see that pressure.
With all levers in neutral, there should be no pressure or very little.
It would seem that if there is air in a cyl, you can not get full extension, If the return line is restricted, things will not work right.
Are the QD's showing full flow when tested.
With the cyl disconnected from the bucket, can you get full extension?