Looked at a media guide last night. We kicked walk-off, last second field goals in TIED games against Cinncinatti at home in 1995 (Doug Pelphrey, crowned Homecoming King, at half-time, kicked a 51 or 52 yarder with 1 second left in the game) and as others have noted, a much shorter kick at LSU in 1998 in Baton Rouge. I was at the UC game in 1995. QB Ryan Hockman (from Ohio) in like 25 seconds of game time, threw two or three perfect 20ish yard passes to a reciever headed out-of-bounds, the last pass setting up the 50 plus yard kick for Pelphrey.
We have ended two overtime games, one an offensive play (Couch pass to Yeast) for the victory against 'Bama in 1997, and on a defensive play (the tackle short of a needed first down) against LSU in 2007.
Heck, going back a long way, one of our top pass defenders of all time, Darryl Bishop picked off a Vandy pass in Nashville, maybe in 1971/72 and returned the pick six for the victory on the game's last play.
I honestly cannot think of a game even being discussed among old timers (I've personally known lettermen dating back to the late 20's) where we were TRAILING and kicked a last second field goal for the victory.