Not to revel in your issue, but I am a little pleased after a few hours of searching to find someone with the EXACT issue (and TV) that began for me 2 weeks ago. I've had the tv about 3 years and had ZERO issues with it until inviting several friends over to watch a football game (of course, lol).
After about 90 minutes of trial and error, it finally was fine...the tests went something like this upon first notice of the shadow screen in the top right corner:
Turned off, waited one minute, turned back on. Result: fine
Ten minutes later, noticed it was back. Turned off and back on quickly. Result: fine - for about a minute.
Turned off, waited 5 minutes. Result: fine - for about a minute.
Turning off seemed to reset things but the duration did not appear to matter, nor how long it stayed 'fixed'.
The past two weeks have had worse occurrences with now there being the horizontal shading issues you noted as well. (I will add pictures next time I'm on as I'm sure tomorrow will come with the same issue).
The only difference I can see between us is I also have times where the screen will have horizontal bars starting at the top (about 3" each), all across the screen and have significant shadow. They appear one after the other but I do not recall them hitting the very bottom row.
Periodically I will wait some simple shadowing out and it goes away if patient. Otherwise my only other hypothesis is the room and the TV are sometimes cooler as I live in a northern climate and do not always keep the room at a steady temperature when not home.
Have you found anything fruitful in your searches? I am also out of warranty but plan to take the back apart after the holiday and see what trouble I can find as I still adore this television...that, and the fact of spending over $3,000 I would like to get 5 years out of it
Thanks for any information you (or others!) can share, I will update if I come across any solutions!