Slim or shim???? Guess it's the same thing....
Running the bubble in the middle of the tweak station DOES NOT necessarily mean your car is tweaked correctly. This just means the car is (weight-wise) is flat. We've found that using the tweak station is a good start, but we NEVER rely on it. Put the car on the track and chances are it's not going to drive with a correct tweak. That is the first step, though. Set the ride height as described by big al. You can then set it on the tweak station and set it, or do the Track Tweak method. Track Tweak is basically setting it on the track and do some hard left and hard right turns. If it's equal, then your chassis and setup is good. If it doesn't, most likely the chassis is twisted. If it hooks harder to one side, you need to adjust the OPPOSITE side to fix the tweak. It takes a little getting used to but it's very effective.