What gears to run?

What is the current tire size? How high can you spin the motor and still make power. Where does the car like to shift now? I am not the biggest mopar rear end guy but I am sure you lost some speed from the 8 3/4 having heavyer parts. I am guessing your MPH is around 102 and if it is your current gear with a 25 to 27 inch tire is around 3.80 to 4.10. But I could use a little more info.