Sorry to hear you were having CPU trouble that may have been caused by Tab Stash. In general, Tab Stash is designed to handle extremely large stashes efficiently (I know of users who have tens of thousands of stashed tabs with no problems), so I'm quite surprised to hear it's not performing well for you.

I'd like to find out more, e.g. exactly what situations led to the high CPU usage, so that I can get to the bottom of whatever is going on. Please feel free to open an issue on GitHub to discuss further: https://github.com/josh-berry/tab-stash/issues/new/choose