It's an automatic. Let the programming (the valve body) figure it out for you automatically.
I have a 6L80 in my truck and I can not tell when it shifts up or down, it is so smooth. Only way I would know would be to put in manual and push the shift button as the tach shift points.
Besides your not likely to even notice with a 383 displacement.
Last edited by Big Dave; 03-23-2018 at 12:59 AM.