We had horrible wallpaper in our house when we moved in. I bought a steamer at home depot, and diff. I scored the wallpaper first with one of the round scoring tools, then used the diff per instructions. It worked, but not well.
Then I mixed 1/2 water and 1/2 cheap fabric softener and sprayed it on, then steamed. It worked very well! Good luck, it's a time consuming process at best.