I decided to try Xplane 10.35, since the last version I tried was 10.25. The previous version ran great on my computer, just silky smooth all around. This time, however, I'm getting a LOT of bad stutter. My framerate is fine - around smaller airports 100+ fps - but I get these regular stutters that I can't figure out. I'll be flying along and then every 5-20 seconds everything freezes up for half a second to a second or so.

 

I'm not using any add-ons or anything yet, and my rendering options are all set very conservatively (mostly defaults, except setting the display resolution.) Like I said, this never happened with 10.25. I noticed when changing the weather around, I get massive stutters while the clouds draw in.. could it be cloud drawing related?

If you are using Nvidia GPU , go to control panel , search for "Threaded optimization" and make sure its off , many people reported that after disabling this Xplane was smooth again.

Thank you so much, I just tried that and it works great... back to smooth again!

Sometimes when you update drivers, the settings get reset.  They shouldn't but sometimes they do.