Dharrison20

I take my truck off roading from time to time and ever since the first time I did my truck has been having a rough idle occasionally.
The truck will shake and my 5.4l v8 will sound like a 6.0l turbo diesel. I'm not sure what it is or what's causing it but as soon as I rev the engine up it will idle like normal again.
And when I take it to the dealership to get it diagnosed of course it doesn't idle roughly. But as soon as I leave its right back at it.
It doesn't do it all the time. Mainly when the engine is still cool and sometimes when I've been in park at a drive through for a couple minutes. Any info would help. Thanks