...or if the torque converter isn't locking properly? Just wondering if a transmission problem isn't masquerading as an engine cooling problem.This is not a good idea unless you double up on the air to oil cooler in front of the radiator and I’m not sure this would be as good at cooling hot trans fluid quickly as the coolant to oil cooler in the radiator.
As stated before, a real time temp gauge in the coolant outlet pipe and one in the transmission oil pan is necessary to see what’s really happening.
Hot trans oil will certainly add to the heat load of the radiator increasing coolant temp. This should be a concern only when the torque converter is unlocked and shearing fluid in warmer weather under the increased demand of towing and/or long ascents where converter lock up can not be maintained.