Have you wet sanded the fin to get all the decals and writing blended in?
Many of the Drake fins are pretty bad unless you blend all the graphic paint overlays
into the foil by wet sanding.
A little work with some 320-480 wet and dry abrasive paper can make a fin that seems pretty bad into a fin that's pretty good.
This does not "always" work but it's definitely worth a try.
Try to find some of the sponge pads with the fine grade abrasive on them.
When used with water, they do a real nice job of "blending" fin surfaces.
Also make sure you are using good fin bolt gaskets to prevent any air from
being sucked down from the top of your board.
Hope this helps,