To the OP, keep in mind that the 777 seats DFW-ORD-DFW are very much sought after by anyone flying these routes. Personally, I would wait an additional hour or two to fly this flight to get:

1. Upgrade to FS suite (so far I've gotten it twice)
2. "Settle" for J seat with Y service

The odds of getting one of these seats on day of check-in are very low due to their popularity by all that qualify for the seats (EXP, PLT, GLD, Y/B fares)