Questions, RE alienware

Hello, I bought an alienware m11x last year, and I have had no problems with it at all so far up until now. I really like this computer but it seems like when I play starcraft 2, on the lowest settings (obviously) it starts to randomly lag from 60 fps down to like 10-20 fps. Which is REALLY annoying. Now I have checked my temps with HWMonitor and they were all around 80. Which seems quite high for this laptop, considering I replaced the thermal paste with some top end stuff. I also play on an external monitor on a very high resolution (1920x1080) or something like that. Would this be the reason that it starts slowing down, maybe because I have the lid closed and am using more computer power on such a high resoloution?