I recently bought a 2005 Durmax. I changed the tranny fluid & fuel filter and was going to change the radiator fluid. I was told to put Dex-cool in. I did a google search on it & found several articles pertaining to a class action lawsuit involving GM & Dex-cool, something about the coolent causing harm to the engine. I believe this was a couple of years back. Can someone tell me what is the reccommended fluid to use?