theschnauzers,
I have a different point of view on this. The NCAA Tournament no longer disrupts CBS in Sunday primetime because they play and telecast those games in the first weekend on other channels. There were no Amazing Race schedule displacements that I recall in March 2011. If you work backwards from the second weekend before Memorial Day (I assume you mean May 20, 2012; if not then it must be May 13), then this is the Amazing Race 20 schedule that ends on that date:
March 4, 11, 18, 25
April 1, 8, 15, 22, 29
May 6, 13, 20