M17x slow after idling

I just received my new Alienware M17x, and it works great... until I walk away for a few minutes.  When I return, my processor is operating at 25% maximum frequency (I'm assuming SpeedStep or some other system is slowing the processor while idle), and when I attempt to do anything else, it won't leave this "idle mode," causing extremely slow performance even when doing something as mundane as browsing the internet.  The computer works fine as long as I keep it busy after starting it up, but I don't want to have to restart the computer every time I walk away from it for more than 5 minutes.  My laptop is plugged in and the power plan set to run at 100%, so that's not the issue.