Hang / move large tv by myself? Is there a tool?

Get a helper. Way too much can go wrong with a jerry-rigged solution. Even the big box stores who do this for a living send two people in the truck. If there were a safe way to do it with one person and a contraption, they would definitely do this to save labor costs, even if it were a very expensive contraption.

Let's see...so you'd rather spend hours putting together an apparatus for what is likely a one-time use, then figure out how to store it for the rest of your life ('cause you're a guy, and it might come in handy at some point in the future) than just ask somebody to help you?  

@fatdaddy2  There are a couple of problems with asking friends. 

1. New neighborhood in new suburb so I don't know many of my neighbors.

2. I need this done whenever I want.  I'm not sure how long it'll take me to do all I need to do behind the tv.  So it could be late night.

3. I enjoy making jigs like this and need to use my tools lest my wife continue to complain about them.

 Unfortunately, I occasionally find myself in a similar situation. If you do have the opportunity to get help, make dam sure they don't become a liability in the process! A lot of people have no idea how work together with another person and there is no time when an accident happens. Explain the maneuver Before it is being done.
 When there is no help and no other choice, I make sure that what ever plan I have is well thought out, often taking advantage of leverage, knowing that I can move an object in steps and not all at once. Making sure that the surface(s) used to help the TV down, are stable and dependable. It is not just the weight, but the awkwardness of the item in that the dimensions, lack of good handholds and balance of the weight of the item are taken into  consideration. Yup, get ahold of the heaviest end for best control.

Hydraulic lift cart. It can also be used for unloading heavy things from a vehicle and raising heavy things onto a workbench. They are pretty darn heavy though, so only really useful if there are no steps.

Husky (Home Depot) sells a hand cranked lifting workbench that can be set up as a desk. I use the 6 foot model as a desk. If you have stairs, you’d probably need to take the top off to move it up and down.