4r70w Transmission fluid return line?

In my car, the top line is the one that sends fluid from the stock cooler to the tranny.

I bought a tranny cooler, one with a fan, a long time ago, but I've never installed it. I'm also thinking of installing a tranny fluid temp gauge, which I'd like to install first.

There are lots of threads about this. Just do a search in this website's forums, and on www.corral.net forums.