my 6.0 with no tuner on it will over heat..well start to i know enough to pull over and let it cool off..if i am pulling my 5th wheel up a steep grade .. and it 100 deg out side... how hot is it out side when this is happens to you ? might just be you need to let off a little and let it cool off. plus is this happing to you and your using your tuner ? if so try it with out the tuner and see if its better