No, fuel cutoff results in a speed drop, as noticed when you floor a 8.1L Yukon, and it tops out at 100. It hits it, falls to 95, and immediatly climbs back up, hits 100, and falls again to 95. Does that every time. As for the cars, I belive its still in the governor of the tranny. There is a check-ball that will cut-off the 4th gear shift signal fluid path when the car reaches a certain speed (controlled by the rotation of the governor). The path is cut off, the tranny won't shift. Some newer ones will also send a signal to the computer to hold the motor from dangerous long periods of time in the redline. Remove this checkball, and at about 4400 rpm, the tranny will shift to 4th, and you will have a whole new range on your speedo to play with.