I wrote the article DaveHess describes.
The brass tee I used has performed fine but there was a bit of work involved making it. The aluminum Acu Temp fitting would transfer heat even faster and should be a quick and easy install, fairly cheap. That's what I would use if I was starting over.
By the way, I towed my 5th wheel about 5K miles in the past month and was able to keep the transmission temp below 195* by watching the gauge and adjusting my foot on the petal. Ambient temps ranged up to 95* on the trip.
Dan