I have the same theory. It never had a problem when new, but it seems to be getting worse as it gets older. Stop and go traffic is the worst for my tranny as it'll run near 210F-250F all the time. Keep in mind I have an auxiliary tranny cooler, but no fan on it. As soon as I speed up the temps come down.

If I'm climbing steep grades at freeway speeds I have to watch the tranny temp and the engine temp. I can control the tranny temp by watching the temperature gauge and going in and out of overdrive. I believe with the OD off the torque converter locks up thus lowering the tranny temp. But, that makes the engine work harder raising the engine temp. It's a vicious cycle.

I've had the overheating tranny and engine problem with the stock fan and the taurus fan. I have since switched back to the stock fan for reliability reasons. Also, I swear that a locked up stock fan puts out way more air at idle than the taurus fan puts out on hi.

The little cooler beside the tranny is the transfer case cooler.

The little pusher fan in front of the radiator is for the air conditioner.

Personally, I don't think an e-fan is significantly more efficient or provides any significant power gains over the stock fan. It still uses energy which comes from the engine.