sounds like it has faded out a bit, your gonna need to polish it all and detail it. try with a light polish and if it doesnt work then move up to a heavier duty polish. if not, you may need to compound it
goof off or goo gone isnt going to remove the "shadows", only the glue, sounds like the paint has faded or is in worse shape than what was under the stickersgoof off or goo gone. wipe on let it set wipe off. then the panel should be a little hazy. then buff it wax it.