I had this problem when the ball was new but also later on too.
When coupler wouldn't release from the ball ws the truck in park with the parking brake on?
Sometimes the ball ends up sitting back a tad too much in the coupler. It can help to move it forward a bit. Usually I can do this by removing the parking brake and putting it in netural. Once in a while I will need to pull forward about an inche real slow so it can release.
Great choice for "Living within my means" and camping for one...
2011 Salem Cruise Lite 20RBXL & 2011 Toyota Tundra Dbl Cab
Camping History: 45 Trips / 133 Nights / 3736 Miles
FRF Social Group: Campers of the West