Every truck owner knows it doesn't matter how powerful or reliable your engine is if you can't get any power to the wheels. If the engine is the heart of the drivetrain, the transmission is its backbone, holding it all together and letting the power flow to the wheels. The transmission mated to your 2001-2010 LB7, LLY, LBZ, or LMM 6.6L Duramax is essential to everything your truck does, and keeping it cool is crucial.
Upgrading your transmission cooler with a Mishimoto performance cooler is a good start, but the fluid still needs to get to the cooler. The stock Duramax transmission cooler lines are fine enough for a new, stock truck, but over time the stock hard lines can begin to degrade.