montyc does not recommend any type of tranny conditioner. it void his warranties for any rebuilds.

I did get a derale cooling pan. It has the cooling tubes in it. I need to put in the temp sender.

That might be your problem with the temp gauge. Water temp gauges are usually thicker. Tranny temp gauges are thinner. you might have to do some custom drilling in the pan.

 

 

Definitely get a temp gauge (either a real trans temp or try the water temp). The factory "idiot" light on the dash for the trans temp will come on when its to late and the trans is already overheated. The gauge the OP posted should work providing the sensor is the proper size/thread. I believe my autometer trans temp gauge has a 1/8" NPT sensor.
I also recommend a good aux trans cooler, the largest size you can afford.