I suspect DB or NAS issue, however...
...if you need to go low level to determine the slowdown, consider downloading sysinternals from Microsoft. Use the tools procmon (very low level access) and procexe to see the loaded dlls. Watch a video or read a blog ,especially on procmon, to know how to use it. It will tell you, in great detail, where performance is being hit. Procexe is like task manager on steroids. It will tell you what is consuming the system when EG is used. It may be an ancillary program.
Procmon will capture EVERYTHING on your machine. Filter. filter, filter until you find clues. Ignore registry read/writes, for example (use buttons at top, right-click items to Exclude). If it is is a low level thing, you can rule it in/out.
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