I've been trying to get the slippery option to work, but for some reason it wasn't working. I finally realized that I've been pressing the wrong "-" key. You need to press the key that's NOT on the number pad. Doh!
LOL, dont worry, your not alone, i did the same thing! Thank God that option is there in the trainer as its the most annoying thing in the game i beleive...apart from the acting