I have a 1989 GT Convertible. I want to put 4.10 rear gears on it but I don't even know where to start with the shift point adjustment. I have a performance chip, but from what I've read, the computer doesn't control the shift points on this car. Adjusting the TV cable wouldn't adjust the shift points either I don't think. So if I have to do anything to change the shift points for the new gear, what is it?