Thanks for the response, Don. I played with the seat for a good half hour at work last night - slid all the way forward, backward, every which way... I lifted the handle, and didn't.... I did everthing except hooking velcro to the back of the headrest and wall of the cab...
.....don't worry there's a happy ending.

Just as I was thinking about getting out some tools, I heard a "click", and the seat latched! I think that the latching mechanism was just hung up, and finally gave in after being jiggled around so much...