I am assuming the fluid level is good.
You said no QD's, so there is nothing to stop the fluid from going to the cyl.
You also said the other cyl work fine, and that tells you that you have sufficient fluid.
Put a hyd pressure gage in the INPUT to the loader valve and tell me the pressure when you try and lift.
If the lift only goes half way and stops at full pressure, you have a mechanical problem.
Can you raise the tractor with the bucket on the ground and tilt the bucket down?
Try this, raise the loader and tilt the bucket down and then try to lower the bucket as far as you can.
If hyd are working good, you should be able to raise the front wheels off the ground using the lift cyl.
Do not go into float.