I have an '06 6.0 and had to have my head gaskets replaced at 10K miles after towing a 13K trailer 4000 miles to Colorado and back. They got it fixed though in nine days under warranty and have had zero problems since. Even had Blackstone labs check my oil and it zero antifreeze in it so al is good. Also, the dealer said that they have had several '05 have the head gasket problem but only had a couple of the '06's. I would stay away from the 6.4 for at least a year and wait on some bugs to get found and corrected. I love my PSD!