Hello Nagual_Sorcerer, thanks a lot for posting your inquire at Intel communities
I’m glad to inform you that your NUC is working as expected. The processor speed in regular use is going to be 1.3 GHz; it is at a particular moment that the processor may reach 2.6 GHz. It will depend on processor load, voltage, power and temperature.
That is called Intel® Turbo boost technology. This feature is engaged automatically depending on those variables.
Also, the maximum Turbo Boost speed won’t be reached by all of the processor cores at the same time, the value is assigned to the cores being used gradually at the moment the Turbo Boost kicks out so it is possible that only one core reaches the maximum Turbo Boost speed assigned by default.
If you change the Turbo Boost frequency multiplier manually then the processor will try to apply it to the cores in use, but if the maximum power allowed (TDP) is already covered, the CPU won’t continue increasing the cores speed to prevent heat problems.
You can change the settings, but we do not recommend.