/cast *Every strike, in seperate macros*
/cast Rune Strike
/script UIErrorsFrame:Clear(); UIErrorsFrame:Show()
^ That's the macro I use on my failDK.
I'm not going to comment on your spec, as a lot of my DK theorycrafting knowledge is outdated and irrelevant. I will say, however, that Icy Touch generates an insane amount of threat nowdays (I see many DK's who use fast weapons and just spam IT and RS, and their aggro is good).
If you need to research fights, use TankSpot! Head up to the Project Marmot forums and read the strats/watch the videos.
As far as gearscore goes, first: ugh. Gearscore is a moderately useful indicator of what raids a person is capable of, but the obsession with it leads people to make horrible gearing choices, especially where trinkets are concerned. If for some reason you WANT to know what your Gearscore is, I wouldn't recommend installing the addon (it would probably give you cancer) but rather check out Wow-Heroes.com (for one gearscore) or Wtfismygearscore.com (for the in-game version of it).