I'm having a hard time getting the coupler off the ball after each trip. I back it in to my garage, there is a slight grade, maybe 5-10 degrees, going up to the garage.

I tried greasing the ball/coupling before going out, I adjusted the coupler nut to be a quarter turn loose after snug, I lift the jack up and down, but the only way to get it off is the chock the trailer wheels, remove the hitch pin and pull the truck forward, then the hitch falls out of the truck and off the coupler.

Any suggestions? What am I doing wrong?

Thanks.