Stay away from Task killers. I switched my phone and I have the one " with google". No task killers and Im doing fine. Not too much lag but its still there. My alarm wasnt going of because I was killing it. I know you have your problem fixed but, I dont download anymore task killers. I dont trust them. And they keep you checking your phone every 5 minutes to make sure things are killed.
This has actually been my one ongoing issue for about a month now that still bothers me. Every week around Sunday or Monday or both sometimes, my phone just randomly turns my alarm volume to zero. Thankfully I downloaded a volume manager that makes it easy to see all my volumes and turn it back up when necessary.
Like I already stated, it seems to be happening around the beginning of the week, every week, and usually it seems to occur around noon, although yesterday (Monday) it seemed like it happened later in the evening. It's just very irritating to have it randomly be turned down so often.