I love the Slivers and am in the process of (slowly) tweaking my deck. You're deck looks like it would work well (it's slivers - they always work well) but I'll give some suggestions that I found helped me;
Creatures;
4x
Crystalline Sliver 
I'd run these and ditch any sliver that has a "target sliver" ability. The advantage these guys give me every time I get them out is unbeatable. I consider these to be a requirement; even if you only run 2 for awhile (like I currently am)
2x
Darkheart Sliver 
No cost; just sac for life. great if your opponent does some mass removal.
2x
Synapse Sliver 
keeping slivers in hand to cast can be hard; this guy helps - especially combined with
Shifting Sliver 
.
2-4x
Talon Sliver 
combine with 2-4
Toxin Sliver 
. It doesn't happen after combat like death touch; your sliver hits first and the creature is destroyed.
2x
Necrotic Sliver 
I would probably ditch either
Muscle Sliver 
or
Sinew Sliver 
to add more effect slivers; 2 more
Heart Slivers 
would help; combine them with Gemhide and you have a happy day.
Land;
4x
Meteor Crater 
Not the best land but in a sliver deck you shouldn't have any problems.
4x
Ancient Ziggurat 
4x
Exotic Orchard 
Not great but if they play more then one colour it can be enough.
I'd also consider running 4x
Overrun 
These are just some suggestions; I'm still trying to perfect mine but I found these guys to be a benefit.
I wouldn't recommend the Rupture Spire - It comes in tapped AND you have to pay 1; you basically lose a turn for that card so it kind of kills your rythum. At the end of the day they're Slivers; as long as you don't load up on all fatties they are a tough tribe to beat and easy to use and tweak as you play.
One last thing, I just read over your deck again and I will say this. If you're already running
Shifting Sliver I'd always have at least 1
Brood Sliver 
in the deck; those free tokens that tap for mana and sac for life can be a real help. Epecially if you drew more slivers ebcause of Synapse Sliver.
Hope that helps man.
