I'm curious as to what type of thread are using. I had a similar problem with my Viking when I used the 1200 yd. spool of Coats and Clark thread. The spool is a large cardboard tube. When the thread would come around it would get stuck between the rest of the thread and the machine. When I'd move the fabric, the extra tension would make it skip a few stitches. The owner of the LQS I took it to suggested the "deelybob." It's a machined piece of plastic that is inserted into the cardboard tube of the spool. This keeps the spool from drooping and causing extra tension.