I've been having this problem with the d3d9.dll, whenever i install it in skyrim at first it was fine, just then when entering interior cell and going back to exterior cell i get fps drops. i will lose 40 of my fps, from 55 fps drops down to 15. even just the d3d9.dll without any effects on this still happens. I tried reinstalling skyrim without mods and problem still persist. I even reset my ini files. I keep wondering why enb d3d9.dll causing this. i found other ppl having this problem as well, and some of them suggested i alt tab out of the game and go back. amazingly it fixes the problem i get my 40 fps back. Still it is very immersion breaking. I wonder if someone could help me so i wouldn't have to alt tab all the time.

There are many topics about this issue and solution to it, search the forum.

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i5-4690k, 16Gb RAM, GTX 1060 6Gb, X-Fi Titanium, Win7 x128
I am INFP, not the brutal, godamnit.