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I am no way connected with Laminar Research just a flight simmer like you.
From reading other postings in this forum frame rates are and have been an issue.
X-Plane 11 is a 64 bit operating system whereas MSFSX is a 32 bit system restricting your RAM to a maximum 4Gb despite how much memory you have in excess of the 4 Gb whereas 64 bit allows the use of greater than 4 Gb.
I am of the opinion your PC does not meet the minimum and recommended specifications. Is it a "gaming" machine used for other purposes or just a "general use" machine.
Have a look at the minimum and recommended specifications at this link http://www.x-plane.com/2016/11/x-plane-11-system-requirements-announced/
Also have a look at this link https://www.youtube.com/watch?v=j_YQMSeNM-M
Hope this helps in understanding why you get the low frame rates.
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