Burning smell from back of truck?

My back smell is from burning the tires up .lol

 

i have the same issue but only when I am backing up, and I am not ridding the clutch, i've tried to look and just can't see where that smell is coming from, Its worst when I am in 4h backing up... my truck has only 3500KM on it.

 

I've had the same issue occasionally , usually after going uphill then stopping , never have figured out what it was , but I think it is grease from the U joints being cast onto the hot exhaust near the transmission