Freddie Mac posted a massive increase in new business volume during August and built up its investment portfolio to its highest level ever. Fannie Mae, on the other hand, saw a continuing freefall in its retained mortgage assets despite a small gain in new business volume. Freddie’s retained portfolio – the $677.76 billion gorilla that gives Fed Chairman Alan Greenspan the jitters – grew by a whopping $17.73 billion in just one month. That reversed… [One data table included]