If you just installed a supercharger, th TV cable might have been inadvertently loosened. Look st the throttle body. There will be two cables goin to it. One is connected to the gas pedal, the other is connected to the tranny. It has a button that allows you to adjust the tension on the cable. When you look at it you should understand. If you don't, you should not be messing with it. :) Tighten up the cable a notch or two. It should firm up your shifts nicely.