I have a similar problem - my TV will drop down a couple of inches while driving from all the road bumps. I've thought about adding a sliding latch of some sort (another Coach owner did it on his Monaco). In my case the TV goes back up without problem (I just need to stop the Coach or wait until I need fuel, then run it back it).
@Tom - But it sounds like your problem is a little worse if the TV won't go back to its stored position without some help. I suspect the motor is worn out.
There is a guy on the irv2 site that has a lift motor available for sale (at least he did a year or so ago).
This is the style motor used - if this looks like yours, and you need one, I can try to get you the contact info for the guy that is (was) selling it. PM me.