A drive spacer is a peice of aluminum that goes between the upper, and lower sections of your outdrive. Its purpose is to lower the propellor into the water further, thus enhancing prop bite, and generally reducing prop slip.
Here is a link showing what one looks like for a bravo:
http://imcomarine.com/ca_store/index...roducts_id=692
There is a delicate balance though. While lowering the outdrive does indeed reduce prop slip, it also increases drag because you now have the outdrive deeper in the water.
I don't know wheather a prop spacer would help your boat or not... hopefully someone with more spacer experience on a Rage will speak up.
Chris