City running slow all of a sudden

Hi @retrochansmith - Usually its all cities, or larger ones that may bog down, but maybe the one causing you problems is running more simulation in the background or something. 

You can clear the cache by deleting the SimCityUserData folder. No worries, it will be recreated when you launch the game. If you just want to clear the actual data files, default locations are C:\Program Files (x86)\Origin Games\SimCity\SimCityUserData\Cache.package and C:\Program Files (x86)\Origin Games\SimCity\SimCityUserData\GraphicsCache.package

You can also Clear Origin cache 

Before redoing the city, here are a few tips that can help to keep SimCity running smoothly:

Firewall and Antivirus - Make sure SimCity.exe and Origin.exe are added to exception lists. If you have BitDefender installed, disable it.
Graphics drivers and Windows OS are patched and updated to newest versions
SimCity.exe and Origin.exe - Set them to run "as administrator"
Nahimic 2 from MSI - this is an audio management program that comes with MSI motherboards. Disable or uninstall it. Nahimic 2 is known to block SimCity from loading
Disable Origin in-game In Origin main menu, right-click SimCity icon, Game Properties, check the box that says "Disable Origin In-game"
Run in Windows 7 or 8 compatibility mode - right-click SimCity shortcut; choose Properties > Compatibility tab > Check the box to run in Win 7 or 8 compatibility mode
Monitor Settings - SimCity does not work with dual monitors, so set it to use one only. Also, no higher than 1080p resolution (no 4k)
No Mods - if you have any installed, uninstall them to see if this helps. 

Definitely post back and let us know whether something worked. If it still won't run, reply back with any error messages you're getting and attach a dxdiag report. How to Dxdiag: https://answers.ea.com/t5/SimCity-2013/How-To-Dxdiag/m-p/634584#U634584

Hope this helps - Happy Building!