200R4 transmission overheating

Last week, i had my test drive with '55 - first time after 10 years - to Istanbul, around 450 kms. from Ankara. I left home around 6am, weather was pretty cool and even cooler in the mountains. I was squeezing the Chevy to around 70-80 mph, without any problems. However i noticed that transmission oil temperature started raising above 180F although i was constantly driving at 4th and w lockup.

The more i continued to drive at 70-80, i observed that temperature raised beyond 210F; which was critical for the transmission since transmission and oil life is completely dependant on pressure and temperature. There is too much conflicting information but what i figured out finally is that temperature is ideal at 175F , occassionally it may go upto 210 while towing, uphill etc. but constant over heat will shorten the life of transmission fluid, decrease the pressures. Also cool oil is not desirable (winter time) 

My observations were:

- Temperature stabilizes at 180F, regardless of weather conditions, while driving at 60 mph

- Going uphill-downhill with overdrive (4th) doesnt affect the temperature

- No engine temperature problems at all w 180F thermostat, outside was upto 40C (105F)

- Lockup doesnt seem to improve cooling

- Driving at Neutral or idling during a break cools it below 180 but not that fast

- I bought an IR temperature reader and my gauge is correct

- Also i observed that lower and upper radiator pan has only 10F of difference, seems that oil from torque converter is heating up the lower part of radiator too

Again surfing the internet, i investigated options:

Theory 1) Installing a deep pan. This has around 2 lt more capacity and bigger surface. I WILL GO THIS OPTION first, and ordered the Hughes deep pan, including gasket and 700R4 filter kit. 700R4 filter sucks the oil from the bottom of the filter, and also not affected with the movements of oil during acceleration. I also ordered a drain plug compatible w my temperature sender, and had it tightened to the hole i have drilled on the side of the pan.

http://www.summitracing.com/parts/HUP-HP3880/?rtype=10

Theory 2) to connect an external cooler after the radiator cooler. the word AFTER is important here, because the oil coming from the torque converter is very hot, and water absorbs very fast its heat and cools down to coolant temperature. Then external air cooler decreases a few tens of Fahreneits. I didn't yet try this option, but if 1 doesnt work, i will additionally install this cooler

Theory 3) to get rid of radiator cooler and only go with external cooler. this theory believes that radiator increases the oil temperature and doesnt allow the transmission to cool down. But then, why are these cars built originally this way? What will happen in winter time w your cold-thick oil in the transmission? 

As a result, now i am with deeper pan, i already saw 10F improvement yesterday but will continue testing. In the mean time, i ordered a fan shroud the decrease the coolant temperature in the radiator below 160F to contribute to cooling.

Lets see together the results.