Sounds just like the 2011 i7 MBP I had or "the cockburner" as it was officially named.
Might be the CPU throttling due to heat. There is no active cooling system on the new MacBook by the looks so I reckon it's thermally managing itself by doing less causing other problems.
Might be the CPU throttling due to heat. There is no active cooling system on the new MacBook by the looks so I reckon it's thermally managing itself by doing less causing other problems.