C6 Shift point adjustment
Check if your tranny has an adjustable vacuum modulator. Pull off the vacuum line and look in the hole. If there is what looks like the head of a small screw in there, it's adjustable. Use a tiny flat screwdriver and turn it clockwise to raise the shift points. It's not reccomended that you go more than 6 turns from the stock position however. If your tranny doesn't have an ajustable vacuum modulator, buy one for it. They're not hard to find, plus they are cheap, and easy to change.