I used to monitor my tranny temp with the senders and a guage. Now, I just use a $40 temp gun from Harbor Freight. I read the temp of the fluid coming into the cooler, going out of the cooler and the outside of the pan.

After doing that a few times in different driving conditions and making a few notes, I have a handle on what the tranny and cooler combo is doing. I occasionally check them just to be sure everything is the same.

I never knew there were so many uses for a temp gun till I bought one.