Can't help with signal but in regards to the sleep of death:
This is just hearsay at the moment but there's a fella that swears the AT&T bloatware is to blame. Mainly the AT&T smart wi-fi app. He claims that his phone has been fine since disabling all the AT&T crap.

I don't know if it's true but I personally disabled all the AT&T apps except "My AT&T" a few days ago and my phone stabilized. I haven't had an unwanted shutdown since.

I've been scratching my head wondering why my phone started acting normal again and then I ran across the posting about the AT&T bloatware and went "Aha!"

 

Disabled (not uninstalled) smart wifi last night...just experienced a shut down

 

Well damn. That totally sucks arse
I'm at a total loss as to why this helps some but not all

 

I found the site and posting where I learned about this.

Post #28

4.0.4 Update - Page 2 - Android Forums at AndroidCentral.com

 

Actually this is what i did, disabled all AT&T apps since im not using it because im here in the philippines and everything works fine, no random shutoff and longer battery life (22 - 24 hours - heavy texting, calls, few minutes internet through wifi and some music)

 

After three shut downs in a day I went to the local Device Service Center (AT&T). The tech acknowledged the 4.0.4 problem and flashed my phone back to 4.0.3.

Three days later and not one power down.

I'm not sure this is helpful, but the only thing to do is get rid of the last update.

 

sharing my "fix".... i did a full battery charge, pulled the battery and let the phone sit for a good 3 mins at least, then put it back in the phone, and did a wipe cache partition, so far, two days with no problems.

This was right after it was restarting over and over again.. i was frustrated, otherwise I probably would've taken the time to properly recalibrate the battery.

 

oh and I did not update the at&t apps, actually don't even touch them.

 

Calling AT&T did not help, as they could only offer a return by mail. That CSR had not even heard of the 4.0.4 bug. I was referred to a service/warrant office in town. I went there and was told their policy was not to flash phones back to previous software versions. They instead replaced the phone which is still on 4.0.3. Whew.