I remember them in ABI while I was there from 80-83, and if I'm not mistaken they were a DL partner at DFW and may have been the precursor to ASA. They fought it out in Abilene with Chaparral (AA) and Texas International.
Quoting Tom in NO (Reply 2): DAYFlyer, I first saw a Rio plane when I connected at DFW on DL back in 1982. A while back, I got to thinking about Rio, and started the following thread. Some good info buried in there for you: