Actually a good point on the trans...
Once it hits about 250F in the pan (probably more like 300F in the valve body), the PCM will cut power. And when trans fluid gets too hot, especially if its old, the torque converter will lose efficiency. Unfortunately the lockup strategy for the 4R100 behind the 7.3L, was programmed to deliver more power, rather than keep the temps low. So it was probably unlocked for much of that climb.
2000 E450 dually V10 wagon