Guess it depends on your location. Here in Fla, I bypassed the Rad and went to the after market then the factory cooler and back to tranny. Picked my gauge signal from the line coming up from the TC before the coolers, I want to know true T/C temp....that is where all the heat is. I found with this setup, pulling a 5500 lb boat, middle of June 95 temp ambient, 65 MPH, stop and go on Florida Turn pike in Miami......never saw it go above 200. We have 140 K miles on this truck, and on second tranny. New tranny (upgaded) and coolers went in around 100K miles. 1999 5.9, QC, 4x4, auto, more new parts than I can list, but a damn fine truck. I am a prevenative Maintenance sicko !