If you've been noodling with mods at all, and haven't emptied the Save folder between the uses of the mods and / or back to Stock, then you are probably dealing with a system that has them all mixed together. The Save folder path is "C:\Users \UserName \Documents \SH4" in simple terms, "UserName" being the log-in name and "Documents" might anyone of several iterations Windows has used over the years. You could also use a "Documents" or "My Documents" short-cut in the file explorer - er, My Computer - er, This PC... delete everything below where that level of the path. This will wipe-out any Saves you have for a Career or Quick Mission, etc., as well as re-setting all of your video and other preferences.
Another thing to look for is that your video stream is "matched". An LCD display has a 'Native' resolution, which Windows will refer to as "recommended". Set your desktop to that resolution, such as 1920x1080. When in the game, use the "Options" menu, "Graphic Settings" and scroll down the drop-down box list in the upper right of that screen to find the resolution that matches Windows'. That is the most efficient it can run. If using HDMI, that should automatically pick-up the correct resolution / frequency for the display.
Another little aspect of the game that wasn't available in the 32-bit Windows XP days was a utility that could flip the header bits on the SH4.exe file that signifies to Windows that the program is capable of addressing more RAM than the old Windows limit of 2G. CapnScurvy (of FotRSU fame) has an excellent article from a fresh Windows 10 install, with a fresh SH4 install, and the use of "Large Address Aware", aka: "LAA". Consult his thread "
Windows10; Large Address Aware; SH4 Install for the details.
Last but not least, think about that 512x TC setting... the world is flying by at that rate, such that 24 hours, or 1440 minutes, goes by in less that 3 minutes (2.8125), or 168.75 seconds... That's not to say that you should or should not be stuttering, but there is a lot going on in that SH4 world you have there...
