I'm sorry, I misunderstood. I didn't realize you were asking about adding a trans cooler to reduce your engine temps.
No, I highly doubt that would work. You need to focus on the engine cooling.
4 things you can look into.
1. Increasing your coolant-cooling capacity. i.e. larger radiator. I know that's not an easy solution, but adding some sort of cooler inline with the heater core lines might be an option (grab a junkyard heater core and plumb it in with a manual water valve....)
2. Increasing the efficiency of your coolant. i.e. changing the antifreeze mix. Of course, use caution, increasing the percentage of water in your system will increase the cooling efficiency, but will also increase the freezing point. IMO this is not an option in MN....
3. Oil cooler. Not much more to say there....I know ones with a thermostat in them exist. Add a little extra cooling capacity to the other fluid in the engine.
4. Increase the airflow. Car engine bays are almost always a high air pressure zone. Lots of air going in, not much coming out. There are hundreds of ways to do this....Everything from spacing the hinges up and removing the rear hood seal to allow air out the back, to cutting/drilling holes in the hood, legit hood cowls, scoops mounted backwards, new vents, junkyard vents etc. etc.
here's a thread with some ideas:
I know a friend of mine added a WRC-style vent right behind his radiator, and it drastically lowered ambient temps in his entire engine bay, lowered average coolant temperatures, and intake temperatures (he had a front-mount IC as well). I'm not sure where he got it, but similar to the real thing seen here: