I have been quietly following this thread as I WAS having the same situation with my 66.I have a fresh engine {stroked sm. block} four speed ,with factory a/c. With a 180 t-stat,170-180 in town. On the highway,200-205 of course with the a/c on. I have a three core rad freshly done, mopar performance viscous fan,and fan shroud. the problem solver was the mr. gasket high flow t-stat, 180-185 all the time :cheers::cheers: