@swcheppes Please move your entire Sims 4 game folder out of Documents\Electronic Arts and onto your desktop. Launch the game, which will create a clean folder with no content. Don't add anything to it yet, just see how the game runs. If it works better than before, the issue is something in your old game folder. It's not likely screenshots, or saves you're not playing, or anything like that; but it could be your current save, or that some of your custom content is now outdated.
If the game still lags in the clean folder, please attach the entire dxdiag to a post. You can upload the whole thing as a .txt file.