Micah, try a load column of about 80 grains of 2F, a single over-powder wad, an amount of shot equal to 100 grains of powder, topped with a thin card wad. That load has done well in almost every 20 gauge I've tried it in.
And I have found that the old saying pretty well holds true "less powder more lead shoots far kills dead"
How thick is the "single over-powder wad" you are using? Thanks.