There have been 14 grand slam walkoffs with the team trailing by 3 runs and two outs. I'm not sure how many of those were hit on a full count though. Adam Dunn was the last to hit such a walk off jack in '06. 9 others were hit with fewer than 2 outs. Some of the names who hit GS with 2 outs and trailing by 3 runs:
1963 Ellis Burton of the Cubs
1970 Carl Taylor of the Cardinals
1973 Ron Lolich of the Indians
1979 Roger Freed of the Cardinals (this one was extra innings)
1983 Bo Diaz of the Phillies
1984 Buddy Bell of the Rangers
1985 Phil Bradley of the Mariners
1986 Dick Schofield of the Angels
1988 Alan Trammell of the Tigers
1996 Chris Hoiles of the Orioles
2001 Brian Giles of the Pirates
Among those that hit walk off GS trailing by 3 with fewer than 2 outs:
1925 Babe Ruth of the Yankees
1952 Bobby Thomson of the Giants
1952 Eddie Joost of the A's
1956 Roberto Clemente of the Pirates
2002 Jason Giambi of the Yankees