Found this over at XDA and it REALLY bumped up my sleep mode battery life.
I haven't had any late text messages by running this, email *may* be delayed until the phone is reawoken. So if you care about that (I don't, I can just activate my phone if I want to check something, since sleep should truly be sleep except phone functions) then you may want to try this and have someone send you an email.
I highly recommend this!
http://forum.xda-developers.com/show...hlight=Battery
Settings>Wireless & Networks> Mobile Network settings "Enable always-on mobile d..."
and also this
Settings>Location>"Use wireless networks"
Unclick both of these and welcome your better battery life while in sleep mode!