2003! The last time they swept both in the same season. Its not an easy thing to do regardless of records for any team to sweep two division rivals, except for the Patriots who I'm sure have done it numerous times. I think we all know this is a less talented team to do it as well, especially on defense, which is a credit to Gase. Enjoy this rare moment! And then hopefully enjoy a playoff berth tomorrow night.
According to these links: http://www.footballdb.com/teams/nfl/buffalo-bills/teamvsteam?opp=17 http://www.footballdb.com/teams/nfl/miami-dolphins/teamvsteam?opp=22 We lost both games to the Bills in 2003. As far as I can tell according to those links the last time we swept both was 1994!! EDIT: I read this wrong.. sorry!
I'm from NY so I memorably remember 2003 was when the Dolphins went 5-0 against New York teams, also beating the Giants. I also remember they missed the playoffs on a tiebreaker with the BRONCOS.... They owe us anyway for allowing them to get home field last season by beating the Pats. That potentially was the difference to Denver making the Super Bowl.