I know how frustrating that is...a few months back I was having trouble it was a different issue..but I had to get a new tensioner.
I have a different machine. But I was wondering if you tried changing the needle size?
Sometimes if you go up or down a size that keeps the thread from breaking. I happen to be a really fast quilter ( fast movement) I use a bigger needle with a smaller thread just so I can go 100 MPH and not worry about thread breakage. You may want to try that. :wink: