I have a 2004 2500HD Chevy. I'm changing the tranny fluid soon. How much fluid does it hold. Not just in the pan, but the whole system? I plan on just changing it with Dexron III. That's what's recommended. Any reason to switch to synthetic? Any tips or advice as I never have done this before? I plan on dropping the pan to drain, then disconnecting the transmission cooler line at the radiator and then starting the vehicle to get the rest of the fluid pumped out. That's How I read it should be done? Do I risk doing any harm to my transmission this way? How long should it take about for the rest of the fluid to pump out once I start the truck? Thanks for any help.