After all of the ramchargers from that period I had, only thing left I could suggest, I believe you should have covered by now, is the common issue of the factory worm clamps on aux trans cooler, which is sandwiched between rad and a/c condensor, seeped oil over time and the dirt and dust would collect on cooler core and rad core, slowing down efficiency big time. You could easily spot that issue after removing that big plastic seal thing.