My Bernina 1230 does not have the ability to change the presser foot pressure. However, it feeds very evenly so I have never had a problem with shifting.
You might want to check the feed dogs on your machine. Take two long strips (jelly roll style) that are cut exactly equal in length. Sew them together and see if the two pieces end up the same length. Also check to see if there is any bend in the strip. Feed dog alignment has a lot to do with how perfectly your machine sews.