2005 f350 diesel, odor upon acceleration?

Recently, my F350 turbo diesel has started to emit a smell whenever I accelerate from a stop. It also occurs if if I get into the accelerator while at cruising speed.

This occurs despite how the a/c is set. The odor is a stinky, sweetish smell. It reminds me of the smell one's car would get whenever the heater core starting leaking antifreeze.

I have looked for but found no leaks.