[f5fstop]

From what you describe, and not being there to actually test it myself, I believe Jake has it right.
Years ago, GM and other manufacurers started programmed a delay into the shift from a forward drive gear to reverse and vice versa. Too many people were rocking their cars and not allowing the engine speed to reduce to idle before the shift. This caused some heavy warranty costs, especially in the winter months.

I know mine has that same feeling, so when I go from drive to reverse I come to a complete stop, engage reverse (foot still on the brake), the start to back up and then I do not have the built in delay.