Turn the tractor off, then turn it on but don't start the engine. Next turn on your third function valve and cycle each of the buttons a few times. Next, move your loader valve in all directions. This will relieve all pressure in the system. Install the 3rd function appliance one hose at a time and it should work fine every time.
Now, if you have pressure built up in the 3rd function appliance, then you should have connected the two ends together so the cylinder will equal out on both ends. All bets are off if the tractor or the 3rd function appliance or tool has been in the sun and the oil in the cylinder and lines has expanded. If that is going to be a problem, then cool it off with cold water.
I have been doing it this way for almost 2 years now and have never had a problem hooking m;y grapple up to the third function valve.