This winter I'm going to make sure to change the ATF and filter in the 2006 Grand Prix. It has 64,000 miles on it now, I'm pretty sure the ATF is original, and it looks alright. Should I just drop the pan, and only replace about half the fluid? Is that a bad idea if I want to put in Dexron 6 synthetic? Otherwise, is it a good idea to unhook the trans cooler lines from the radiator and let one pump the old fluid out while the other sucks new fluid in? Any advice appreciated.