Illustrator CC 2017 one core usage (MacPro late 2013)

Hello all,

I'm using a new Mac Pro late 2013 on which illustrator runs very slowly. Especially with opening and saving files, locally and on the server. When saving or opening a file i see the CPU usage 100% on illustrator, which is 9% of total CPU availability. Approximately a third of RAM is being used and 20% of GPU. 

Certain files can take up to 5 minutes to save or open!!

If i compare the above performance with Felix, i see CPU usage around 400 - 500% and in render up to 1200%(!).

For some reason Illustrator is using 10% of available performance. Does anybody experience the same issue?

Things i tried:

PS printers added and tested

both startup and normal disk are available (190 - 200 gb free space)

MacPro configuration:

3,5 GHz 6-Core Intel Xeon E5

16 GB 1866 MHz DDR3

AMD FirePro D500 3072 MB

OSX Sierra (10.12.5)

Thanks in advance!