I've had my M15 since mid December and from the get go I've experienced thermal throttling.
Under games and stress tests, both HWInfo and Intel XTU would indicate temperatures would reach 100°c and thermal throttling.
Closer inspection showed this was mainly on half of the cores, 0, 2 and 4 in HWInfo.
After researching possible causes and finding that the thermal paste application could be a factor, I followed the Alienware process of repasting, but I just faced the same situation. I left it a week or so to give the paste chance to settle in, but the high temperatures in half the CPU cores remained. I tried another repaste just to make sure that wasn't an issue, and had the same problem.
Since then, I have had to undervolt and reduce the max turbo of the cores to keep the temperatures of the 3 hot cores under control.
So currently, the maximum temperatures I see are reasonable, but I am still left with half of the CPU cores being significantly hotter than the other half. The 3 hot cores will hit maximum temperatures in the region of 10-15°c higher than the cooler cores.
I've recently read and been advised that this could also be a symptom of an issue with the heatsink.
As the laptop is new and still under it's warranty, is it possible to have a replacement heatsink sent out? I am happy with doing the actual swap myself.