I have a 2003 6.0 and have had this problem for several years. No dealer has been able to figure it out. Not always but usually when pulling my car trailer it will gasp for air and buck making a swooshing sound. I look in the mirror at the exhaust and every time it does it, it puffs black smoke. Like it is gasping for air. A friend told me he thought it was something to do with a waste gate. Does this truck even have a waste gate? I can't make it do it on demand so it is really hard for the dealer to diagnose. Never any codes. Any help?