Frustrating, isn't it. I worked at tension for an entire day and it is finally correct. Sounds like your bobbin tensin might be a little too tight. However, my first suggestion to you is: Put in a new needle. Sometimes if they are a little dull, and that seems to make weird things happen. My machine performs best FMQ if I use jeans needles (size 16).
You probably have some new needles on hand, but if you don't have a jeans needle, replace with a new needle -- the biggest you have, and see if that helps a little.
amh