Running hot

i have always tested fan clutches by driving the car till it is warmed up then pull over and feel how much air its pushing. you say it looks like you have good coolant flow so by the issue in stop and go traffic the only difference would seem to be air flow? or you could even see if its an air problem in your driveway by letting the car warm up then put a good house fan on high in front of it and see if the temp drops. also check your carbs idle mix, could be a couple small things making a big problem.