Hello Kenny,
I have tried what you suggested regarding the nav range. Although I was curious at first thinking it would cure the problem, this has helped me cross out one more item off my "tried-but-no-change" list which is something I'm going to pile up and send to the developers.
As for the "Declutter" softkey, I leave it as it's shown on my screenshots above.
If nothing works out in the end, I will try and install the aircraft into P3D V3 once again. My first attempt was utterly unsuccesful leaving the whole system laggy and overstressed.