If you can see holes in the fabric where there should be a stitch, your problem is skipped stitches. This is a machine or needle issue, not an IS problem. Clean your sensor wheels and track to ensure they are riding in the proper position. Check sensor wheel O-rings for cracks. If there are large cracks, they will need to be replaced. O-rings can be purchased from www.quiltech.com.
Check connection jacks at sensor wheels for looseness. Check motor belt and brushes. New motor brushes can also be ordered from www.quilttech.com.
For Gammill machines, as a last resort you can check sensor wheel screws for tightness. Do not attempt this unless all other options fail.