Are you using a topstitch needle? How about size 14? When you start to FMQ on a large project after doing small practice pieces there is a tendency to be more concerned with managing the bulk of the quilt rather than managing the amount of the quilt that is in your quilting area-perhaps there is drag around the needle area. Another possible problem is the speed you are sewing-because of the size of the quilt you need to slow down to maintain control. Please don't change your thread but try the suggestions that I know you will be receiving as the ladies of the board wake up for the day.