It's been just under a month since I got my Vivid and posted here the same issues you guys were experiencing. Want to know the true *fix* ?
To put it bluntly, the factory ROM image is jacked up. Plain and simple. Over the past couple weeks I've become involved with a group who builds custom ROMs for the Vivid. The results have been phenomenal, and the benefits plentiful. Since rooting my phone and switching to a third party ROM:
1) The reboots have stopped. Completely.
2) The phone is faster and more responsive.
3) There's no more Carrier IQ tracking software on my phone. Google it.
4) The bloatware apps installed by AT&T are gone.
5) More.. much more.
If you feel like learning something and actually seeing this device perform the way it should, I urge you to check it out. The ROM I'm using is the Illuminati 3.5 ROM by Wild Child on xda-developers. Go to google and search for xda-developers Illuminati. Should be the top link. The whole process of rooting your phone may seem scary and dangerous, but honestly it isn't that bad - especially once you read a bit and understand how it all works. It doesn't require a rocket surgeon
This isn't an advertisement of any form or fashion, just posting my experiences and resolution.