Goo Gone is similar, but i have used WD-40 with good success. You have to soak it pretty good and let it sit for a while, but it shouldn't hurt the plastic/paint underneath.
Another thing to try, but also to
BE VERY CAREFUL WITH, is some stuff called "oops!" It's a cocktail of all kinds of aromatic solvents that you will definitely want to test on an inconspicuous area of the cab before use. Some plastics it doesn't bother, other will cloud or get gooey from it.
If your test shows that it is compatible with the plastic, lightly wet the sticker with the stuff and when it soaks in, try to peel it off. Afterward, use some some soapy water on it, rinse and let it dry. If there is a little haze, some plastic polish will fix that.
The above should be used only as a last resort, BTW

Good Luck.
RandyT