OK, a major update to my previous comment. As a last-ditch effort, I tried deleting and rebuilding my rolling cache. Amazingly, that did the trick. Went back and flew in the same area and same weather conditions that had been a stuttering mess before, and they are now perfectly smooth. And I noticed a few new graphical assets I hadn’t noticed before doing this, like the rays around the sun in a clear sky. So now I’m thinking that maybe some of the new graphics assets from the update couldn’t load, or were otherwise impacted by old assets remaining in the cache. Just another guess, but all I know is that it worked. Phew!, minor stroke averted.
Incidentally, while I was at it I also increased the size of my rolling cache from 8GB to 32GB, but I doubt that had anything to do with the improvement. It was likely just the cleaning out of old stuff. Fingers crossed now that it stays this way.