For a while now I've suspected TS3 frame drops and stutters due to high frame rates and the CPU unable to process 100-300+ fps on a single thread.
Recently (a few months now) Nvidia has had a feature to limit frame rates on any application or game. I have found something that fixes all lag in game, with all expansions enabled without mods. For years people have fixed maps of routing issues and Twallans mods have been a must to get the game to even semi playable.
Right so we know how The Sims 3 is with even half of the expansions enabled.