2012 GMC Sierra, Plug Fouling again

"AFM" was screwing things up. It's a V8 motor, but engineers thought that it should run on 4 cylinders for fuel efficiency...hence the "Automatic Fuel Management" system.

This causes spark plugs to foul up, that causes rough idling, loss of power, and the truck to shake...oh...and LOSS of gas mileage for "efficiency".

Once the Range Technology was plugged in so that all 8 cylinders were forced to operate, BOOM...smooth idle, more power AND a 2MPH+ increase! It went from 16.1 to 18.1 and up to 19. It was a different truck!