Is your fabric a poly/cotton? How about the type of batting you are using? Is some of the quilt tied before your machine quilting? I have been fortunate with my pin basting, but I also make sure to quilt slow enough to let the walking foot do its’ job to feed the whole sandwich through evenly. It seems we all find what works best for us, have you cleaned the feed dog area on your machine recently? Just some thoughts as I read your post.