EDH Sliver deck

I'm not going to pretend to be an expert on EDH, given that I've just started tinkering with it myself.  However, I have a few thoughts:

Demonic Tutor is a must for most decks, but unless you add something that you REALLY need into those remaining cards, I'm not seeing the sense in it.  Assuming Sliver Overlord is your general, you can tutor up any sliver you want without needing the tutor.  Now, if you toss in either Door of Destinies or Coat of Arms, well, to say the least you would want to tutor those up.

As for what to put into the deck, I would first suggest a decent collection of removal spells and/or board wipes.  Just because EDH is a lot more laid back than standard or modern doesn't mean having several removal spells doesn't really help - and, in many cases, a soft removal spell can actually be more effective than a hard one.  For instance, if your opponent has their general out, if you kill or exile it, it just goes back to the command zone and can be recast, but if you cast Pacifism/Defang/Arrest on it... now it's still in play, but is just pretty much useless.

The second thing I'd suggest is some added mana-fixing.  I'm thinking Rampant Growth, Ranger's Path, Seek the Horizon, Nature's Lore, Chromatic Lantern and even mana dorks (if you're desperate).  I know Gemhide Sliver helps there, but you cannot expect it to live long if people see what you're doing.

Third, I'd suggest some solidly defensive cards (as you will almost always be the biggest target first).  So toss in Norn's Annex, Aetherize, and things of that nature to reduce any/all attacks against you.  Keep in mind that most players do NOT pack enchantment hate in their EDH decks, despite the higher prevalence of enchantments in EDH play.

Lastly, Amoeboid Changeling can be hilarious in a sliver deck, as it lets you make another creature into a sliver, which you can then take with Sliver Overlord - this includes their generals.

Remember to have fun with it.  EDH games will often see some pretty ridiculous stuff going on, so don't be afraid to throw some weird stuff into your deck either.

Psh... actually getting the cards and playing... what fun is that?