OptiPlex 7040 Micro with a Intel i7-6700T , slow CPU

Hello,

I have a OptiPlex 7040 Micro with a Intel i7-6700T under Windows 10
It uses the origial PSU, but has 1 samsung 960 Pro 1TB m.2 SSD and 1 2.5" Samsung 950 Pro 256GB SSD.
And the ram are Corsaire 32GB (2x16GB) 2133mhz.....

The problem is when I have a 4 threads (plex transcoding, or folding@home) the cpu runs at around 80% usage on task manager and only about 2/1.9Ghz instead of 2.8Ghz base clock or boost.

Single or dual thread task get more than 3Ghz.... I don't believe it to be a thermal issue as the cpu even running @80% load all threads at max 70°c.

I did see that under CPUID HWmonitor the package usage of the CPU is not going past 20W... is it holding back for some reason?

Any idea?

Thank you.

Alex