I have the same setup. The old 4 speed 4R100 sometimes needs to be downshifted. What was the tachometer reading when you had the over heat? On steep mountain roads I do not hesitate to let the engine idle and cool off or let the brake rotors cool off either by the side of the road.
The old transmissions are dependable but only have 4 gears. The rebuilt ones now being offered by companies like BD, have a new style of torque converter and stronger parts. They cost about $5,000 but would greatly increase the performance of the 7.3. The price is high but not compared to buying even a used 6.7. I am thinking of making the move at 175 k miles.
