Can you go from one custom tune to an other,with out going back to stock?
I think you have to go back to stock first.

 

No, you don`t have to go back to stock first. You may move between tunes freely. You do have to return to stock before updating the software in the SCT.

 

The X3 tunes will hold up to 3 custom tunes, plus your stock tune.

You can move between the custom tunes freely, only takes couple mins to upload.

 

Thanks snaf2u & Franchi for your replies. The other day I went from 91 performance to stock, then 91 street tune. I guess I did not need to go back to stock first. The shifts in the 91 performance were a little rough, nice and smooth in the street tune.