2013 Ford Explorer, Weak acceleration that suddenly kicks into full power.

I've had a car do this before and I never found the answer on it either.

My 2013 Ford Explorer will bog down when you initially put it under heavy acceleration from low speed. The engine will rev up and sound normal, except that it feels severely restricted until it hits around 40mph, and then while still in the same gear, the car will suddenly surge to full power and accelerate properly, feeling a very distinct shift in inertia and the engine very noticably picks up.

A second symptom is when this happens, it is usually accompanied by a distinct gunpowder smell, like you get when going through several AR mags.