ProTools 12 Ultimate - CPU Overload without playing

[Aquic]

Hi there,
I have been mixing a band with more than 300 tracks by session among audio tracks (full orchestra, drums, percs, guitars, keyboards, etc...), auxiliars, Vcas, individual masters, busses, etc... I have been using PT 12.3-PT 12.6 so far, although I have already used the new ProTools Ultimate in the last two mixes, that did not solve my problem either.

In all the mixes, the CPU was placed at 50%-60% without being in Play. I even had to reset the whole system several times, because my computer was unable to play. This never happen in my life with my old Mac Pro. The CPU always was around 20% even in the case of the more busy mixes.

I'm using a complete updated High Sierra version, as well as a new Mac Pro 3,5 Ghz 6-Core Intel Xeon E5, with SSD hard disk, 64 GB 1866 Mhz DDR3, etc...

Any ideas about what is happening? Because it's crazy that my New amazing mac is close to exhaustion, when its power surpasses my old Mac a lot!

Thanks in advance!