It changes the shift points of the transmission. When accelerating or decelerating, it will shift at a higher speed that normal. This will give better performance in hilly terrain, but will sacrifice fuel economy. In flat areas, you might just as well leave it off.
Retired electronics engineer. Avid paddler & birder.
2011 Silverado 2500HD, diesel, 4x4,crew cab, 8' bed
Palomino Puma 253FBS (27' 5er) & '94 19' Class B