Found the problem by calling the manufacturer of the hitch tongue mechanism, Titan. The particular model has what's called a handle, not one of the "trigger" releases like on most tongues these days. It's attached to the top of the coupler case assembly with a pivot pin which allows the handle to move up and down. Then there's a 5/16" bolt that inserts through two holes in the handle, just behind the pivot pin, that holds the ball catch coupler down when the tongue is on the ball.
That 5/16" bolt was missing, and to my knowledge, and I've owned the boat for six years, there's never been a bolt there. I finally just decided that I've been extremely lucky all these years that the tongue didn't come off the ball when I was towing. Scary feeling. Anyway, I got a bolt, inserted in the proper holes and put a lock nut on it, and it worked. I just don't know how it worked all this time without the bolt in place, so I may be mistaken and somewhere along the way it came out, but I sure don't think so.
Mystery solved. Bob at Titan was really helpful incase you ever need their help. Thanks to all of you who offered tips. Wish there was a way to insert pictures of things on this site to help people see what someone is working on.
