You can run the slipper MUCH looser than you would think on the FS2.
Set the rear diff so the slipper slips first but only just, set the front diff just a fraction tighter than that and your good to go. Most people you feel my slipper on the bench say it MUST be slipping on track ... hardly at all, just silky smooth Kyosho goodness
(I run a one-way in the front as you know but that is how I used to run the diff at the front before going back to what I'm most comfortable with ... a one-way)