You've had some good replies. My suggestion would be to go to a larger needle. Sometimes when you're going through thicker quilts, the thread "pulls" too tight when it goes through the fabric and then doesn't make the loop underneath that the bobbin hook needs to catch to make the stitch. = dropped stitches. That, and go slowly. Sometimes we rev up the machine to get through the thick stuff, but it needs extra time to work right.
If you're still getting dropped stitches with a 80/12 needle, go up to a 90/14.