I always have the truck about 1-2" higher than the pin box so that when I back up under it the box pushes the truck down just a tad and it locks in every single time. If The hitch happens to be about level with the pin box (where it doesn't put any pressure on the truck while backing under it) then my hitch usually won't latch all the way or it goes half way and I have to inch forward, reverse, forward and the handle latches.
Unloading, I just chock the trailer tires and dropping the front landing gear until I am raising the truck about 2" or so. Usually that releases enough pressure that the handle unlatches easily, a couple times I have to put the truck into neutral and it will roll back just a small amount and that will release some pressure, pull the handle and pull out.
LOL and be sure to pull completely out from under the trailer, I have the self leveling system on mine and I had the truck about 1" under the trailer and when the trailer started leveling, the front dropped down and just barely sat on the bed rail. No harm, just a durrrr moment.