I would get those experienced installers back out there and show them the problem. If not, and the unit is less than 90 days old it is in warranty. Sears will probably charge you to correct an improper install.

I called the installers back. They came and blamed it all on the type of door and opener I have. They did try to fix the header that had pulled loose from their shoddy work and told me to not adjust the chain any more saying "it's ok for it to sag." BS. After they left I operated it twice and the header then had a 1 inch gap behind it and of course the chain was again loose enough to drag on the top edge of the door. I looked down the rail and could see a significant ammount of downward bow. I called him and only got a message. Later in the day he called and admitted it was a poor install! So he agreed to fix the header right and get the right rail for an 8' door and only charge me a total of what Sears would have charged which is $119.00 plus tax. I'll believe that when I see it.
Yard.