I am having the exact same problem. After three days it started to get worse. Now it will cut out during a call and soft reboot every once in a while. When the screen goes blank like you discribed, I had to hit the soft reboot button twice to get it to reboot.
I called tech support for Sprint, and they are sending me a replacement phone that is coming Wednesday. I assume it is a hardware problem interfacing with the new update in a not so nice way.
I searched all the different forums and have not seen any solutions.
I will keep hope for someone to tell us what exactly is going on...