The two chemicals you see most places are DIF and 3M Wallpaper and Paste Remover. For the DIF to work, the paper should be scored with a Paper Tiger or other tool. For 3M Wallpaper and Paste Remover to work, it must be applied a certain way, using 3M's applicator. You must allow the recommended time for any chemical to loosen the paper. I find steamers more tolerable in the dead of winter, when you need more humidity in the house.
Instructions are also important when using a steamer.
Unless you wait until a lot of steam is coming out of the nozzle, it will not lift the paper. You can paper over well-adhered paper. The trick is to prime the old paper first, with wallpaper primer, and use a busy enough pattern to hide the seams of the first paper. Wallpaper primer seals the surface to be papered and will allow the paper to stick better and be easier to remove. Since the surface is sealed, the water is not prematurely sucked out of the paste, nor does the paste soak into the surface, so the paper is easier to remove later.