Excess heat is the #1 killer of transmissions. For individuals who tow, race or simply run their diesel hard, proper cooling of your transmission fluid is one of the most important things that you can do to increase the life of your transmission. When the mainline pressure is increased with upgrades such as a high-performance transmission kit, your transmission generates additional heat. A PPE 6.6L Duramax Performance Transmission Cooler is critical in such situations.