There is a product called Tal Strip that I can guarantee you will take off anything you want taken off. However, it will also take off any paint or other coating it comes in contact with. It is a paint stripper made primarily for removing paint from aluminum airplane parts. It is a concoction of several different kinds of solvents and will remove paint in a hurry but doesn't harm the metal. I'm pretty confident it would release those decals and the old adhesive but be warned is is caustic stuff. You need heavy duty rubber gloves, safety glasses, and preferably a Tyvek suit on when you work with it. You don't want it on your skin as it will burn, don't ask me how I know . You can find it at auto parts stores such as Advanced Auto. It comes in a spray can or a bulk liquid form. It might be an option but if you are going to spray it make sure you cover anything you don't want it in contact with. I would hate to see what it might do to a screen on a fish finder or a plexi-glass windshield on a console.