Thanks for the suggestions.  I think the problem is mostly the denim fabric but I will try all of these suggestions next week when I can get back to it.  When I first brought my machine home I stitched out most of the designs and was amazed at the great results with these stitches.  But that was with cotton and stabilizer.  I even tried it again on that same piece of fabric and can't get the same results.  At the time I knew very little about my machine and used nothing special in the way of thread.  I think I'll also check to see if I can adjust the tension successfully on other stitches.  Maybe it's somehow stuck in the middle.  I think I may even try some of the old invisible thread that I have.  I guess it's possible that I used that originally but it looks like I just used white bobbin thread.  Unfortunately I should have stitched out the stitches with black on top and white in the bobbin but I used all white.  Someday I'll try them all again..  Thanks again.
Ceil