I have 77W flight DFW-MIA legs in October.
Looks like a guarantee upgrade at this point -- only 11 J/F seats are sold on the way out; 6 J/F seats sold on the way back. Weirdly, a lot of the other A321 and 737 flights appear much fuller in both coach and F.
Roundtrip DFW-MIA tickets are $100 in coach, $900 in First.
Unfortunately, the grace of low fares are never bestowed on us outstations -- Adding in the E145 SWO-DFW legs (i.e. same dates SWO-MIA) brings the fares to $400 on the same flights in coach, $1150 in F.
(and those E145 legs are still only half full; not exactly a situation of limited space)