Most often causes of low fps or stuttering for DAI is either it is too much program for your hardware, hardware overheating, or something else is running and taking CPU/GPU when DAI needs it.
1) You tried lowering specs BUT....did you have anything like Nvidia game control that may override in game specs? Also you may want to delete the files profileoptions and profileoptions_options which are located inside your game Saves folder which is usually in the Users section of Windows.
2) Get a program like afterburner, or speedfan, and monitor your hardware temps. You are checking to see if something is heating up and may have a need for cleaning or repair.
3) Use task manager or https://docs.microsoft.com/en-us/sysinternals/downloads/process-explorer to monitor what programs are using CPU and see if something is running when you are playing.
Keep us updated and you may also want to post a DxDiag per the sticky at top of forum.
