Just to be clear, it is sticking when you go to unhook? If that is the case, realize it often gets bound up when you jack up the front of the trailer, so as som have suggested you can move the truck slightly forward, or sometimes backward and it will release. But what I find easier, MAKE SURE THE WHEELS ARE CHOCKED and you're jacks are on the groun, is the unlock it before I start to raise the trailer. That allows the pin to move freely during the lift process.
If that situation is not the case, usually a good coating of grease will help.
2013 F-350 SRW 6.7 Powerstroke
2015 Jayco HT 29.5BHDS