Cooling Issue

I'm having trouble keeping my 340 cool when stopped at a light. It runs right at and doesn't get above 190* while cruising, but will creep up steadily to 210, 220 and further etc while stopped. I have a 22" champion 3-row radiator with sealed factory shroud and 17" clutch fan with Hayden shorter thermostatic clutch. Considering the ambient temps are only about 65-70, I want to get this fixed before the hot temps come.

Considering it cools when cruising (the temp gauge even cycles as the thermostat opens and closes), the radiator is fine, right? That just leaves a potential air flow or water flow issue, right? I do have a factory fixed fan I can try, but would rather stick with the clutch fan. Could my parts store water pump not be up to the task? What do you folks think? I'm wondering if buying a high flow water pump and thermostat may cure this issue.

Oh yeah, I'm running 60/40 distilled water/coolant mix and it's got plenty of ignition timing in it. Thanks!