I'm using the exact same sandwich I had at the dealer. As to thread/needle. I'm using the Topstitch 90/14 recommended by Superior. I have King Tut top and bottom, which the dealer said was just fine - I'll switch the bobbin out today for Bottom Line or So Fine and see what happens.
Tension is set on auto which is the recommended and what we were using on the dealer's machine.
Have tried feed dogs dropped and feed dogs covered.
And I haven't graduated to cones of thread yet. :)
I'll be trying some other options today.