Sounds like you car runs fine (engine heat) while you're at cruising speed but heats up in traffic.
FWIW, here is a method used by several SOCers (myself included) to help keep an engine cooler in higher temps while in traffic.
Here is the method that Terry Nuckels used. Inexpensive and super easy to install. Others have posted many variations of this method, but Terry's is the simplest.
I've McGuyvered a similar engine lid prop on my car. It helped keep the engine cooler in heavy traffic.
Ultimately, having your engine free-flowed and installing a remote oil cooler with thermostat fan is best. Until then this method should help your issue. Hope this helps!