[Haulin'Green]

I'm still learning about diesels so bear with me. I had my '04 6.0 with no mods, pulling the gooseneck up a pretty steep grade with about 12k behind it. Started to struggle pullin the load and then I heard this sound, kind of like a vacuum lea,, just a change in the sound coming from the engine, then no more than twenty minutes later after dumping the load in the gooseneck everything returned to normal. This has actually happened twice, both times on the same hill with the same load, but cleared up both times after emptying the trailer.

 

[my03psd]

Maybe it was your cooling fan cycling?It's been described as a roaring kind of sound.