This will fix the frame slowdown/stutter. I did not make this, nor do I take responsibility for any part of it. I had the problem with Wildfire and this fixed it! So any moderator deciding to remove it, feel free to do so. But at least explain whyin a pm or something. I scanned the files with VirusTotal and it seems fine. Best assurance I can provide.

Originally the files were in an .exe, I dug through. Version 1.1.37. If that helps.
(https://community.jaggedalliance.com/forums/topic/18-want-to-get-feet-wet-with-ja2-while-you-wait-for-ja3-but-the-game-is-slow-and-stutters-like-mad-fix-here/)

The links for the files:

https://1fichier.com/?i0kjsmukm6lvrxbs8rcb

and another, just incase you prefer it

https://www.mediafire.com/file/lvrctnmazx756dj/JaggedAlliance2Fix.zip/file

Simple enough to use. Text instructions in the zip. Short version is to add the 3 .dll files into the game folder and for reasons I do not understand, it just fixes the problem. Go figure. Enjoy the game!