See if you can get a sharp pointed knife (I used my hunting knife) poke it under the paper and try to slide it between the paper and the wall.
The key is to try and get the outer layer of paper off by peeling, leaving a paper backing on the wall, which will then be scored and should come off easier.
DIF gel works well for me, but each wall is unique and depends heavily on what wall prep was used to hang the paper, type of paper and glue, age of paper, etc.