My 07 Silverado idles in V8 mode

 

As I understand it, at low speeds(even if you're just rolling/coasting) and idle (as pointed out) the AFM won't activate, because there's not enough power to turn a half-dead crank and pistons. Which means good for us - becuase we won't lose that rumbling idle.

 

More psychological than anything else....you use very little fuel at idle as opposed to cruising, even on half the cylinders. It's like taking the antenna off a car to reduce wind drag...you'll never notice it.

 

Good to know, thanks for the responses!!