Another thing to check is the height of the quilt in relation to the bed of the machine. You should be able to slide your fingers between the quilt on the take-up rail and the machine bed. If it's too low or high you will get broken thread and/or skipped stitches. The quilt needs a bit of bounce in it. I usually move my take-up rail every other row or at most every third row. Good luck.
Darren