Due to the large number of demons, NUTS.WAD can struggle to run on some PCs, here are some methods that I personally found to boost the framerate:
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Don't use GZDoom. Out of every port I have tested, GZDoom seems to struggle the most, even with the graphics turned all the way down. Strangely enough however, this issue is not present in older PCs.
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Kill the hit-scanners first. Enemies that utilize hitscan in large quantities can drop the FPS considerably. Get rid of them as soon as possible; the BFG is recommended for this process due to it's ability to wipe out weak enemies on a massive scale. There is no shortage of plasma cells either, so don't be shy to use it.
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Lower your screen size. Lowering your screens display size can increase the FPS dramatically. Only use this method if all other listed options didn't work, I also wouldn't put the screen size smaller than 5 because anything smaller than that is simply absurd.
Hopefully this guide helped you make your game look less like a slideshow. In case you were wondering, my source-port of choosing for NUTS.WAD is LZDoom, as it runs the best of all other ports I have tested, (although this may vary depending on your PC.)
Here is an example of a run that utilizes these techniques: Notice how I fire a single BFG shot into the chaingunners? This helps the framerate soar during the first section.