While playing one of my characters I noticed that when I walked up to the word wall at Autumnwatch Tower it gave me two words of power and in my shouts menu I now have two Drain Vitality shouts only the wrong one is actually marked for death this is beat up but the description it gives is that of the drain vitality WTF!

IIRC, there are 2 walls there? That or I encountered the same glitch. I can't be more specific as this was months ago, but when reading your post a little red flag came up and i'm sure I got 2 shouts or something when I was at Autumnwatch.

It's a bug. Here:
Marked for Death page: http://www.uesp.net/wiki/Skyrim:Marked_for_Death
Drain Vitality page: http://www.uesp.net/wiki/Skyrim:Drain_Vitality

I have a feeling I may not be getting anymore new shouts now