Over heating 66 Dart

I chased this problem years ago. Not the radiator, it cools fine on the highway. Had a shroud, still overheated at idle. Tried clutch fan, still overheated at idle . Tried a factory flex fan, never overheated. Removed shroud, never overheated. Now I run 3 row cores in original radiators, flex fans, no shroud, never overheats. Yeah I know, overkill. Summer is hot everywhere, lame argument. I have lived from SD to SC and FL. Cooling is the same.