I am looking at getting the Nitto Terra Grapplers either 275/70/18 (33.3")or the 295/70 18 (34.4"). Will they fit on my stock suspension and will I have much mileage loss compared to the 285/60/18 (31.3) I have on the X now?

I was looking at the Dura Grappler as well but I don't think the I like less aggressive look with my XD Black Rockstar wheels.

 

I am running 295/75/16's on mine. Mine sits a tad higher than stock and the fronts rub the inner back fender well plactic when turned fully. Only actually heard it once, but you can see it.